Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Semi-insulating gallium arsenide-deep trapping levels, dislocations and backgating Tang, Wade Wai Chung 1984

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1985_A7 T36.pdf [ 5.45MB ]
Metadata
JSON: 831-1.0096300.json
JSON-LD: 831-1.0096300-ld.json
RDF/XML (Pretty): 831-1.0096300-rdf.xml
RDF/JSON: 831-1.0096300-rdf.json
Turtle: 831-1.0096300-turtle.txt
N-Triples: 831-1.0096300-rdf-ntriples.txt
Original Record: 831-1.0096300-source.json
Full Text
831-1.0096300-fulltext.txt
Citation
831-1.0096300.ris

Full Text

SEMI-INSULATING GALLIUM ARSENIDE-DEEP DISLOCATIONS AND  TRAPPING LEVELS,  BACKGATING  by WADE WAI CHUNG TANG B.Sc,  A THESIS SUBMITTED  Simon F r a s e r U n i v e r s i t y , 1982  IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES  i n the Department of E l e c t r i c a l  We accept  t h i s t h e s i s as conforming  Engineering  to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA December, 1984 ©Wade Wai Chung Tang, 1984  9?  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree at the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may  be granted by the head o f  department or by h i s or her  representatives.  my  It is  understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be allowed without my  permission.  Department of  ELECTRICAL  ENGINEERING  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  E-6  (3/81)  DEC. 2 3 , 1984  written  ABSTRACT  Work i s r e p o r t e d  on three  topics relating  back the development of GaAs i n t e g r a t e d trapping  l e v e l s i n the  Deep t r a p p i n g  circuits.  These t o p i c s are deep  s t a r t i n g s e m i - i n s u l a t i n g GaAs, the e f f e c t of  d i s l o c a t i o n s on d e v i c e i n f l u e n c e of v o l t a g e s  to problems which hold  c h a r a c t e r i s t i c s , and on nearby c o n t a c t s  backgating.  on d e v i c e  (The  latter  performance).  l e v e l s i n undoped s e m i - i n s u l a t i n g  liquid-encapsulated—  C z o c h r a l s k l GaAs grown i n the <100> d i r e c t i o n were c h a r a c t e r i z e d p h o t o c u r r e n t deep l e v e l  By u s i n g  Cr  photocurrent-DLTS i n the  p r e v i o u s l y used i n t h i s l a b o r a t o r y , and This  t r a p has  not  encapsulated-Czochralski The  GaAs by u s i n g  measurements on an a r r a y of MESFET.  device  hence to observe the  p r e v i o u s l y been observed i n undoped  i n v e s t i g a t e d using  f a b r i c a t i o n processes,  the  c h a r a c t e r i s t i c s and  established.  temperature range  temperature range than  the d i s t a n c e  liquid-  device  a d i s l o c a t i o n e t c h procedure  Due  s c a t t e r was  trap known as  photocurrent-DLTS.  p o s s i b i l i t y of an e f f e c t of d i s l o c a t i o n s on  c h a r a c t e r i s t i c s was  Three  e l e c t r o d e s , i n s t e a d of Au-Ge e l e c t r o d e s , i t  became p o s s i b l e to extend the experiment to a higher  EL2.  using  t r a n s i e n t spectroscopy (photocurrent-DLTS).  e l e c t r o n l e v e l s were found using 200K to 400K.  i s the  and  to problems i n c o n t r o l l i n g the  such t h a t no to n e a r e s t  However, s c a t t e r of t h r e s h o l d  c o r r e l a t i o n between d i s l o c a t i o n would  v o l t a g e was  larger for  devices  f a b r i c a t e d on areas of honeycomb-like d i s l o c a t i o n s network as opposed a r e a s w i t h unconnected wavy l i n e s of d i s l o c a t i o n .  be  to  -  iii -  B a c k g a t i n g (which causes unwanted communication investigated  between d e v i c e s ) was  i n c o n j u n c t i o n w i t h s u b s t r a t e c o n d u c t i o n measurement.  was proposed f o r the e f f e c t as present i n the d e v i c e s used i n t h i s experiment.  A model  -  iv -  TABLE OF CONTENTS  P age ABSTRACT  i i  LIST OF TABLES  v  LIST OF FIGURES  . . . .  ACKNOWLEDGEMENTS.  ix  1.  INTRODUCTION  2.  OVERVIEW OF SI GaAs  3.  4.  5.  6.  vi  1 '3  2.1 2.2  Introduction S u b s t r a t e Compensation Mechanism  3 4  2.3  The Nature o f the Deep Donor L e v e l EL2  5  PHOTOCURRENT DEEP LEVEL TRANSIENT SPECTROSCOPY  7  3.1  Spectroscopy  7  3.2 B r i e f Reviewof P u b l i s h e d Work on PhotocWent-DLTS 3.3 B a s i c P r i n c i p l e s of Photocurrent-DLTS. " 3.4 E x p e r i m e n t a l Procedures 3.5 R e s u l t s DISLOCATIONS AND DEVICE CHARACTERISTICS  11 12 16 21 38  4.1 4.2 4.3  Introduction B r i e f Review of P u b l i s h e d Work D e s c r i p t i o n of Mask and D e v i c e F a b r i c a t i o n  38 39 44  4.3.1 4.3.2 4.3.3 4.3.4  46 46 49 49  I n t r o d u c t i o n to Deep L e v e l T r a n s i e n t  Substrate Preparation I o n Implantation Post-Implant Anneal Metallization  4.4  Measurements  4.5  Results  BACKGATING  •  50 54  IN GaAs  68  5.1  Introduction  . . . . .  68  5.2  Experimental  Procedures and R e s u l t s  70  CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK  84  REFERENCES  86  APPENDIX  93  - v LIST OF TABLES .  P age 3.1  V a l u e s of Ep and a c a l c u l a t e d from F i g . 3.15 the drops d e t e c t e d  for  by photocurrent-DLTS  3.2  R e l a t i v e peak h e i g h t of PI  4.1  Settings for Si N  4.2  S e t t i n g f o r oxygen ashing u s i n g Plasma-Therm system  3  1 +  to P2  f i l m d e p o s i t i o n by PECVD  34 37 47 48  - vi LIST OF FIGURES  Page 3.1  3.2  B a s i c p r i n c i p l e of Capacitance-DLTS ( a ) Steady (b) T r a p f i l l i n g c y c l e ( c ) T r a p emptying c y c l e  state 8  T r a n s i e n t c u r r e n t observed f o r sample 184-Cr a t 300 K. E x c i t a t i o n l i g h t pulse turned o f f a t t = 0 sec  13  3.3  B(= rmax/t^) v e r s u s «(= t / t )  17  3.4  Absorption of l i g h t  18  3.5  Sample s t r u c t u r e s used i n photocurrent-DLTS  2  A  (670 nm) i n GaAs a t 300 K  (a) p l a n a r s t r u c t u r e (b) t h i n sandwich  experiment  structure  3.6  B l o c k diagram of photocurrent-DLTS  3.7  Vacuum chamber used i n the photocurrent-DLTS experiment Graph of Temperature vs dark leakage c u r r e n t and r a t i o of p h o t o c u r r e n t to dark leakage c u r r e n t o f (a) sample 63T42 (b) sample 51-Cr  24  A photocurrent-DLTS Window = 40 ms)  spectrum f o r sample 51-Cr (Rate 26  A photocurrent-DLTS Window = 40 ms)  spectrum f o r sample 86-Cr  3.8  3.9  3.10  3.11  3.12  3.13  3.14  3.15  set-up  20 .  22  23  (Rate 27  A photocurrent-DLTS spectrum f o r sample 152-Cr (Rate Window = 40 ms) . . . .  28  A photocurrent-DLTS spectrum f o r sample 184-Cr (Rate Window = 40 ms) . . .  29  A photocurrent-DLTS spectrum f o r sample 86-T ( p o s i t i v e b i a s , Rate Window = 20 ms)  30  A photocurrent-DLTS spectrum f o r sample 86-T ( n e g a t i v e b i a s , Rate Window = 20 ms)  31  A c t i v a t i o n energy p l o t photocurrent-DLTS  33  f o r t r a p s d e t e c t e d by  - viiP age 4.1  E t c h p i t s t r u c t u r e i n sample 283-S11 showing ( a ) honeycomb-like network and (b) wavy l i n e s  40  4.2  Mask f o r d e v i c e  45  4.3  Fabriation  4.4  MESFET a r r a y on sample 283-S11 ( m a g n i f i e d 300X)  4.5  I  DS DS - V  c  n  a  array  sequence f o r the MESFET a r r a y  r  a  c  t  e  r  i  sample 283-S11.  t  V  i  G g  c  s  o  f  MESFET from d e v i c e  bias:  -0.2V/step  57  Typical 1  4.7  V a r i a t i o n of V a c r o s s the three MESFET a r r a y s on sample 283-S11 MESFET a r r a y a f t e r d i s l o c a t i o n e t c h ( a ) L e f t h a l f o f the a r r a y showing network s t r u c t u r e (b) R i g h t h a l f o f the a r r a y showing l e s s e r o r g a n i z e l i n e s t r u c t u r e  4.8  4.9  4.10  4.11  4.12  4.13  G S  55  a r r a y on  4.6  D S  -V  s  51  c h a r a c t e r i s t i c f o r sample 283-S11  58  f c h  P l o t of V vs distance sample 283-S11 T R  to nearest  59  60  p i t f o r MESFET from 61  Histograms o f the d i s t r i b u t i o n of V * f o r FET along the ( a ) L e f t h a l f of 3 r d a r r a y ( F i g . 4.8) ( b ) R i g h t h a l f o f 3 rd a r r a y  63  Histograms o f t h e d i s t r i b u t i o n o f leakage c u r r e n t f o r FET along the (a) L e f t h a l f of 3 r d a r r a y (b) R i g h t h a l f of 3 rd a r r a y  64  P l o t of V v s l o c a l d i s l o c a t i o n d e n s i t y for. MESFET from sample 283-S11  65  t  t  P l o t of I  h  D  S  (@ V  G g  = OV) v s l o c a l d i s l o c a t i o n d e n s i t y  f o r MESFET from sample 283-S11  66  5.1  MESFET o f sample 45-592  71  5.2  MESFET o f sample 123-5131  71  5.3  B l o c k diagram o f backgating  5.4  T y p i c a l Ij)g~V g V varying D  G  experimental  s e t up  73  c h a r a c t e r i s t i c s o f sample 123-5131 w i t h 74  - viii Page 5.5  T y p i c a l I s~ DS c h a r a c t e r i s t i c s V  D  o  f  sample 123-5131 w i t h  Vgg v a r y i n g  75  5.6  T y p i c a l Ijjg-VQg c h a r a c t e r i s t i c s of sample 123-5131  76  5.7  Typical I  77  5.8  Typical  p l o t of I  D  S  vs V  B G  f o r sample 123-5131  78  5.9  Typical  p l o t of I  D  S  vs V  B G  f o r sample 123-5131  79  5.10  Typical  p l o t of I  B  G  vs V  B G  f o r sample 45-592  81  5.11  Typical  p l o t of I  R  r  vs V  R r  f o r sample 123-5131  82  _ D S  V  G S  c h a r a c t e r i s t i c s o f sample 45-592  ACKNOWLEDGEMENTS  I  thank my s u p e r v i s o r , Dr. L. Young, f o r h i s p a t i e n c e , guidance, and  encouragement  during  the course of my work.  Dr. W. L a u and Mr. K. Lowe are thanked f o r t h e i r h e l p f u l a d v i c e and Mr. D. Hutcheon  i s thanked f o r h i s a s s i s t a n c e i n f a b r i c a t i n g  i n the d i s l o c a t i o n  the d e v i c e  array  experiment.  I thank Messrs. I . Abdel-Motaleb, S. Dindo, W. D u r t l e r , D. H u i , and K. Tan f o r t h e i r h e l p f u l d i s c u s s i o n s . a s s i s t a n c e i n preparing  Mr. D. H u i i s a l s o thanked f o r h i s  some o f the f i g u r e s as i s Mr. S. Dindo f o r h i s  a s s i s t a n c e i n the DLTS experiment. A p p r e c i a t i o n i s a l s o due to Mr. G. Needham of Cominco L i m i t e d , B.C., who s u p p l i e d the GaAs wafers; Messrs. A. Leugner and L. K j o l b y , who maintained  the equipment  i n the lab;' and Ms. C h a r l o t t e Stevenson, who typed  the m a n u s c r i p t . F i n a n c i a l support provided  by the B r i t i s h Columbia S c i e n c e C o u n c i l and  by the N a t u r a l S c i e n c e s and E n g i n e e r i n g Research C o u n c i l of Canada i s gratefully  acknowledged.  1  CHAPTER 1 INTRODUCTION  The  need f o r high  frequency c i r c u i t s i n systems such as  microwave telecommunication and research  i n gallium arsenide  l a r g e s c a l e GaAs IC substrates Among the  and  integrated  circuits  promoted a c t i v e  (GaAs I C ) .  to be f e a s i b l e , homogeneous, t h e r m a l l y  a well-characterized  (LEC)  GaAs i s emerging as the best  semi-insulating  so t h a t the  ( S I ) wafers can be  occur i n Cr-doped SI  for  stable required.  liquid-encapsulated-  choice.  One  advantage i s  produced without chromium doping,  s e l e c t i v e multiple d i r e c t ion implantation  a p p l i e d without problems due  I n order  f a b r i c a t i o n process are  s e v e r a l c r y s t a l growing techniques a v a i l a b l e ,  Czochralski that  super-computers has  radar,  process can  to the r e d i s t r i b u t i o n of Cr  h o r i z o n t a l Bridgman (HB)  [1,2]  grown GaAs.  be  such as  Chapter 2  gives  a overview of SI GaAs. It f o r IC the  i s d e s i r a b l e that,before  a s t a r t i n g wafer i s used as a  f a b r i c a t i o n , the deep t r a p p i n g  thermal s t a b i l i t y  should  be proven.  o b j e c t i v e of the work which was received  The  second o b j e c t i v e was  d i s l o c a t i o n s on d e v i c e  characteristics,  Chapter 3  2  be known  covers the  and  first  p h o t o c u r r e n t deep l e v e l  GaAs as  transient  to i n v e s t i g a t e the e f f e c t s of  c h a r a c t e r i s t i c s . LEC  t y p i c a l l y lO^-lO^/cm .  spectrum should  to c h a r a c t e r i z e undoped SI<100> LEC  from Cominco by a method c a l l e d  spectroscopy.  density,  level  substrate  GaAs has  a high d i s l o c a t i o n  I f d i s l o c a t i o n s should  affect  device  t h i s h i g h d e n s i t y would become a major problem.  t h i s , an a r r a y of m e t a l - s e m i c o n d u c t o r - f i e l d - e f f e c t - t r a n s i s t o r s  To  study  (MESFET)  and  Schottky  pads was designed  and f a b r i c a t e d .  Chapter 4 d e s c r i b e s the  measurements made to seek a c o r r e l a t i o n between d i s l o c a t i o n s and d e v i c characteristics.  The t h i r d  substrate conduction  o b j e c t i v e was to study  and backgating  the phenomena of  i n SI s u b s t r a t e s .  Backgating  can  harmful to the o p e r a t i o n of IC because i t indue es unwanted c r o s s t a l k between d e v i c e s .  The e f f e c t of backgating  and the c u r r e n t - v o l t a g e  c h a r a c t e r i s t i c s o f e l e c t r o d e s on SI GaAs i s d i s c u s s e d Finally,  chapter 6 c o n t a i n s  i n Chapter 5.  the summary and c o n c l u s i o n s .  3  CHAPTER 2 OVERVIEW OF SI GaAs  2.1  Introduction GaAs t e c h n o l g i e s have r e c e i v e d i n c r e a s i n g a t t e n t i o n over the past few  years  f o r high frequency  applications.  over S i f o r IC f a b r i c a t i o n a r e :  The two b a s i c advantages of GaAs  1) the higher  e l e c t r o n m o b i l i t y and s a t u r -  ated v e l o c i t y i n GaAs can provide a two to s i x times p o t e n t i a l speed advantage over S i , and 2) the a v a i l a b i l i t y of GaAs as a s e m i - i n s u l a t i n g g i v e s b e t t e r i s o l a t i o n between d e v i c e s Si.  substrate  than the p-n j u n c t i o n i s o l a t i o n i n  D i r e c t i o n i m p l a n t a t i o n i n t o SI s u b s t r a t e s i s p r e s e n t l y one o f the  b e t t e r techniques  f o r GaAs IC f a b r i c a t i o n .  Formation o f the a c t i v e r e g i o n  by i o n i m p l a n t a t i o n i n SI s u b s t r a t e s i s d e s i r a b l e because of i t s p o t e n t i a l as a r e l i a b l e , ity,  high y i e l d  and low c o s t technology.  However, the inhomogen-  and v a r i a b l e q u a l i t y of SI GaAs s u b s t r a t e s i s a major l i m i t a t i o n at  present. The [3,4].  production  of SI GaAs by the HB technique  I n the HB technique,  GaAs i s s y n t h e s i z e d  vapor t r a n s p o r t o f As from an elemental boat.  i n s i d e a furnace  to Ga c o n t a i n e d  by the  i n a quartz  The c r y s t a l growth i s i n i t i a t e d by moving the boat s l o w l y down the  furnace end.  source  s t a r t e d i n the 1960' s  i n a temperature g r a d i e n t  so as t o c o o l down the GaAs melt from one  SI i n g o t s are produced i f Cr i s added to the melt p r i o r  to c o o l i n g [3]  o r i f the i n g o t s a r e exposed to an oxygen atmosphere i n the growth ampoule [4].  4  Liquid was  e n c a p s u l a t i o n was  first  demonstrated by Metz et a l . [5] and  developed by M u l l i n et a l . [6] to produce GaAs i n g o t s by the LEC  nique.  I n the LEC  growth  tech-  technique, the GaAs melt i s c o n t a i n e d i n a high-  p u r i t y q u a r t z or p y r o l y t i c boron n i t r i d e c r u c i b l e , and e n c a p s u l a t e d w i t h a l a y e r of molten B 0 . 2  3  The presence of the B 0 , t o g e t h e r w i t h h i g h argon 2  3  p r e s s u r e on top, prevent s i g n i f i c a n t l o s s of As d u r i n g c r y s t a l Growth i s i n i t i a t e d  by immersing  a GaAs seed through the B 0 2  3  growth. into  the melt,  and the c r y s t a l i s grown by slowly withdrawing the seed from the m e l t . the seed and  the c r u c i b l e are r o t a t i n g  Both  during the c r y s t a l p u l l i n g p r o c e s s .  An important advantage of the LEC method i s t h a t SI i n g o t s can be a t t a i n e d without any i n t e n t i o n a l doping.  Another a t t r a c t i v e f e a t u r e of the LEC  technique i s t h a t the i n g o t s produced can be c y l i n d r i c a l  shaped w i t h l a r g e  diameter, whereas the i n g o t s from HB method are the shape of the boat (D shaped) w i t h the diameter u s u a l l y l e s s than 2 i n c h e s . of LEC  i s that i n g o t s produced g e n e r a l l y have a f a c t o r of 10 h i g h e r  d i s l o c a t i o n d e n s i t y as compared to those grown by  2.2  The main d i s a d v a n t a g e  S u b s t r a t e Compensation  HB.  Mechanism  The SI behaviour of GaAs i s g e n e r a l l y b e l i e v e d compensation of s h a l l o w i m p u r i t i e s by deep l e v e l s by M a r t i n et a l . [7] i n d i c a t e d a deep donor l e v e l ,  to be due to  [7-9].  A model proposed  that compensation comes from the presence of  l a b e l l e d as EL2  [ 1 7 ] , i n undoped m a t e r i a l s , and from  t h i s deep donor l e v e l and a C r - r e l a t e d deep a c c e p t o r l e v e l i n Cr-doped materials. N  needed  For undoped m a t e r i a l s , the c o n c e n t r a t i o n of deep donor  levels  to a c h i e v e SI behaviour can be determined from the charge  5  neutrality  equation  d e r i v e d by Johnson et a l . [ 9 ] :  n2+n(N - N „ ) - n . A D 1  "(WW"  -N  2  1 1  c  (2.1)  !  where n, N., N^, and N _ are the c o n c e n t r a t i o n s A D DD tors,  o f e l e c t r o n s , shallow '  shallow donors, and deep donor l e v e l s ( E L 2 ) , r e s p e c t i v e l y ,  i n t r i n s i c c a r r i e r concentration, N conduction constant  v  n^ i s the  i s the e f f e c t i v e d e n s i t y o f s t a t e s i n  band, E -E i s the a c t i v a t i o n 'C EL2  energy o f EL2,  k i s the Boltzmann  and T i s the temperature.  According  the E q . ( 2 . 1 ) , w i t h  N  A  ~  N  D  10 cm~ , Johnson e t a l . i5  =  b e l i e v e that the s e m i - i n s u l a t i n g behaviour (n,p i s between 1.5xlO cm~  when  accep-  i5  3  and 5xlO - cm . J  6  -3  3  « 1 0 c m ) can be obtained 7  -3  Holmes e t a l .  [8]  found  t h a t the c o n c e n t r a t i o n o f deep donor EL2 i n GaAs depends on the As c o n c e n t r a t i o n i n the melt d u r i n g growth. about 5 x l O c m i 5  to 0.51.  - 3  to 1.7x10 cm" 16  3  The EL2 d e n s i t y i n c r e a s e d  from  as the As atom f r a c t i o n i n c r e a s e d from 0.48  I n a d d i t i o n , SI m a t e r i a l s can be obtained  o n l y i f the As  c o n c e n t r a t i o n i n the melt l i e s between a atom f r a c t i o n of 0.475 and 0.534. Below the c r i t i c a l As c o n c e n t r a t i o n (0.475) excess a c c e p t o r s , w h i l e  the m a t e r i a l was p-type due to  the r e s i s t i v i t y decreased  s h a r p l y above 0.535 As  atom f r a c t i o n as a r e s u l t o f an i n c r e a s e i n the f r e e - e l e c t r o n c o n c e n t r a t i o n c o n t r i b u t e d from the h i g h deep donor  2.3  concentration.  The N a t u r e o f the Deep Donor L e v e l EL2 EL2  has been observed, by v a r i o u s techniques,  i n bulk and vapor phase  6  e p i t a x i a l GaAs [15,17,23,26,52] and  I t s thermal a c t i v a t i o n  energy  can  be  expressed as [ 7 ] :  AE = E  The In  - E  = 0.759 - (2.37  thought  c o n s i d e r e d to be an a c c e p t o r .  grown by the HB  into  to be due  to oxygen and  arose because SI GaAs can  of EL2  density.  Holmes e t a l . [8]  suggested  i s probably a s s o c i a t e d w i t h an i n t r i n s i c d e f e c t such as an As site.  i s c r e a t e d i n a two-step  Lagowski e t a l . [12] at MIT process:  1) a Ga vacancy  the l a t t i c e ' d u r i n g c r y s t a l growth, and 2)  a n t i s i t e d e f e c t As Holmes et a l .  [13], E l l i o t t Ga  Ga  [8].  of c u r r e n t debate.  an As  non-  to oxygen i n which the d e n s i t y of o x y g e n - r e l a t e d t r a p s  t h i s vacancy  suggested  i s incorporated interacts  an As atom d u r i n g the post growth c o o l i n g / a n n e a l i n g process to form  al.  be  out i n an oxygen  A paper by Huber e t a l . [11] gave evidence f o r the  i n t e r s t i t i a l and a Ga vacant that EL2  incorrectly  T h i s mistake  are an o r d e r lower than t h a t of EL2 t h a t EL2  (2.2)  -  t e c h n i q u e , p r o v i d e d the growth i s c a r r i e d  atmosphere [ 4 ] . assignment  -1  donor n a t u r e of t h i s l e v e l had been proven by M i r c e a e t a l . [ 1 0 ] .  e a r l i e r work t h i s l e v e l was  was  x IO *;* *}! eV  . The  with the  T h i s model i s supported q u i t e w e l l by the r e s u l t exact o r i g i n of deep l e v e l EL2  is still  of  a subject  I t i s g e n e r a l l y b e l i e v e d by authors such as Webers e t et a l .  [14], and Lagowski e t a l . [12]  a n t i s i t e d e f e c t w h i l e M a r t i n e t a l . [15]  d e f e c t complex i n v o l v i n g As  .  that t h i s l e v e l i s  favour the model of a p o i n t  7  CHAPTER 3 PHOTOCURREMT DEEP LEVEL TRANSIENT SPECTROSCOPY  3.1  I n t r o d u c t i o n t o Deep L e v e l T r a n s i e n t Deep l e v e l  i n 1974.  the  (DLTS) was i n t r o d u c e d  In i t s original  conception,  the b i a s V ( t )  of a Schottky  ( o r p-n j u n c t i o n ) i s r e p e t i t i v e l y modulated from forward  temperature of the sample i s v a r i e d .  pulse,  I n the forward  traps i n the d e p l e t i o n region are f i l l e d  reverse  by Lang [16]  I t i s a method of i n v e s t i g a t i n g deep t r a p p i n g l e v e l s i n  semiconductors. diode  t r a n s i e n t spectroscopy  Spectroscopy  to r e v e r s e as  b i a s p o r t i o n o f the  with c a r r i e r s .  During the  b i a s p o r t i o n of the p u l s e , t r a p s i n the d e p l e t i o n r e g i o n a r e emptied  at a r a t e which depends upon the t r a p ' s energy l e v e l E^,, c a r r i e r r a t e e and the temperature T o f the sample.  emission  The l i b e r a t i o n o f these  trapped  c a r r i e r s r e s u l t s i n a r e l a x a t i o n of the d e p l e t i o n width and hence a transient of capacitance The  with a p a r t i c u l a r  t r a n s i e n t capacitance  boxcar averager a t two p r e s e t  C(t)  i s processed  sampling times t  times d e f i n e a r a t e window o f the system. time c o n s t a n t  o f a deep l e v e l equals  reaches a maximum.  time constant  i  T ( F i g . 3.1).  with a dual  and t 2  These two sampling  At a p a r t i c u l a r  temperature, the  the r a t e window and AC = C ( t ) - C ( t ) x  DLTS. scan,  2  Thus, a peak i n the spectrum of AC v e r s u s T i s o b t a i n e d .  U s u a l l y peaks w i l l appear i n the spectrum, each c o r r e s p o n d i n g particular  channel  trap l e v e l .  This original  to a  form of DLTS i s known as c a p a c i t a n c e -  By s e l e c t i n g d i f f e r e n t r a t e windows and r e p e a t i n g the temperature a s e t of ( T , T ) can be obtained  for a particular  trapping  level.  V(t)  time  B  (b) •  p  •  +  0  ue ©  n  DLTS  TRANSIENT  time F i g . 3,1 Basic p r i n c i p l e ( c ) T r a p emptying c y c l e  of capacitance-DLTS  (a) S t e a d y  state  (b) T r a p f i l l i n g  cycle  9  From the p r i n c i p l e of d e t a i l e d balance,  the time constant  of a t r a p  can be g i v e n as ( w i t h an assumption of s i n g l e degeneracy)  x =  where AE = E the  (ayT ) 2  = E  n  c  exp(AE/kT)  - 1  (3.1)  - E_ ( t h e energy d i f f e r e n c e between c o n d u c t i o n T  t r a p p i n g l e v e l ) f o r e l e c t r o n traps w i t h y = 2 . 2 8 x l O c m S K ~ 2 0  AE = Ep = E ^ - Ey  band) f o r h o l e  capture  cross section.  traps w i t h y = 1 . 7 x l 0 c m ~ S K ~ 2 l  Eq.  £n(T x) = M  (3.1)  (I)  2  -  - i  of that p a r t i c u l a r  trap.  N  C  {2C  From t h i s s i g n a t u r e l i n e ,  and  a y-axis  the s i g n a t u r e  line  the a c t i v a t i o n energy AE The  trap density  can  [19]:  AC-(AC) } 2  OO  C (C 2  from DLTS scans) of  This line i s called  the f o l l o w i n g equation  D X  the  [18], and o i s the  2  ( d a t a obtained  c r o s s s e c t i o n a can then be r e s o l v e d .  using  N, T  [17], or  (3.2)  t r a p , a s t r a i g h t l i n e w i t h a slope of AE/k  c r o s s i n g of -£n(o"Y) can be o b t a i n e d .  be estimated  2  *n(cTY)  2  the c a p t u r e  2  can be r e w r i t t e n as  So by p l o t t i n g Jin ( T T ) versus 1/T  and  - i  and  ( t h e energy d i f f e r e n c e between the t r a p p i n g l e v e l and  valence  a particular  - 2  band  (3.3) -C  )  2  10  where  i s the net i o n z e d donor d e n s i t y , C  the b i a s i s changed from  forward  q  i s the c a p a c i t a n c e r i g h t  to r e v e r s e , C  after  i s the c a p a c i t a n c e when the CO  e qN  1/2  2  t r a n s i e n t reaches  steady  s t a t e , AC = C  - C , and C, =  capacitance corresponding  o»  X  A l d e r s t e i n [20] The  l  p  J  T  other types of DLTS have  Channel conductance DLTS (C-DLTS) was i n 1976.  2(E -E )  to the n o n - i o n i z e d r e g i o n of the d e p l e t i o n l a y e r .  S i n c e the i n t r o d u c t i o n of capacitance-DLTS, been d e s c r i b e d .  i s the  {7^=——-r}  The  s t r u c t u r e used  p r i n c i p l e of C-DLTS i s v e r y s i m i l a r  presented  i n t h i s technique  by  i s a MESFET.  to t h a t of capacitance-DLTS  with  the  e x c e p t i o n t h a t the change i n d r a i n - s o u r c e c u r r e n t of a MESFET i s monitored i n s t e a d of the change i n c a p a c i t a n c e of a S c h o t t k y d i o d e .  These two  of DLTS are o n l y a p p l i c a b l e to c o n d u c t i v e s u b s t r a t e s w i t h c a r r i e r s by e l e c t r i c a l means.  For SI s u b s t r a t e s , where the f r e e c a r r i e r  t i o n i s v e r y s m a l l , photocurrent-DLTS termed as o p t i c a l photo-induced  can be used.  to h i g h r e s i s t i v i t y  injected  concentra-  Photocurrent-DLTS,  t r a n s i e n t c u r r e n t s p e c t r o s c o p y by Hurtes  transient  kinds  et a l . [21]  and  s p e c t r o s c o p y by Fairman et a l . [22], i s a p p l i c a b l e  s u b s t r a t e s w i t h c a r r i e r s generated  optically.  d i r e c t i m p l a n t a t i o n i n t o SI s u b s t r a t e s ( e s p e c i a l l y undoped LEC g i n g as the l e a d i n g technology are w e l l worth s t u d y i n g and  f o r IC f a b r i c a t i o n ,  photocurrent-DLTS  With  grown) emer-  t r a p s i n SI s u b s t r a t e s  i s a u s e f u l method to  i n v e s t i g a t e these t r a p s . I n s e c t i o n 3.2,  a b r i e f review of photocurrent-DLTS  on SI GaAs i s  presented w h i l e i n the r e s t of the c h a p t e r , the experimental procedure  of  11  photocurrent-DLTS  and the r e s u l t s o b t a i n e d from undoped SI <100> LEC GaAs as  r e c e i v e d from Cominco are d e s c r i b e d .  3.2  B r i e f review o f p u b l i s h e d work on photocurrent-DLTS Some o f the p u b l i c a t i o n s on traps i n SI GaAs d e t e c t e d using  rent-DLTS  are:  B o i s [23]; Fairman, O l i v e r and Morin [22,24,32];  photocurDeveaud  and Toulouse [25]; I t o h and Y a n a i [26];' Rhee, B h a t t a c h a r y a and Koyama [27]; Yuba, Gamo and Namba [28]; Ogawa, Kamiya and Y a n a i [29]; and O l i v e r , and Chen [ 3 0 ] .  Photocurrent-DLTS  was a l s o a p p l i e d  Fairman  to e p i t a x i a l l a y e r s on  top  o f SI s u b s t r a t e by H u r t e s e t a l . [21,31]; Yuba e t a l . [28]; Fairman e t  al.  [22,24,32] and I t o h e t a l . [ 2 6 ] .  photocurrent-DLTS  are l i s t e d  Traps d e t e c t e d by these a u t h o r s u s i n g  i n the appendix.  The t r a p t h a t i s b e l i e v e d t o  be a s s o c i a t e d w i t h C r , which was l a b e l l e d HLI by Mitonneau g e n e r a l l y found i n C r doped samples  et a l .  and absent i n undoped samples.  e l e c t r o n t r a p EL2, which plays a c r i t i c a l  [18], i s The  r o l e i n the s e m i - i n s u l a t i n g  behaviour o f undoped GaAs s u b s t r a t e s , has been found i n SI GaAs u s i n g photocurrent-DLTS al.  [31].  o n l y by M a r t i n et a l . [ 2 3 ] , I t o h e t a l . [26] and H u r t e s e t  However, only M a r t i n e t a l . a p p l i e d photocurrent-DLTS d i r e c t l y to  SI GaAs s u b s t r a t e .  H u r t e s e t a l . used  samples w i t h an undoped vapour  e p i t a x i a l (VPE) GaAs l a y e r on top of Cr-doped  SI GaAs (The undoped  phase  layer  e x h i b i t e d a h i g h - r e s i s t i v i t y r e g i o n near the s u b s t r a t e , whereas the remaining part was c o n d u c t i n g and n - t y p e ) .  As shown i n the appendix, f o r  H u r t e s e t a l ; EL2 was found i n n-type VPE w i t h h i g h r e s i s t i v i t y on SI GaAs and not i n h i g h r e s i s t i v i t y  buffer  layer  b u f f e r l a y e r on SI GaAs, so EL2 i n  t h i s case was p r o p e r l y p r e s e n t i n the n-type VPE l a y e r .  The s t r u c t u r e  which  12  was  used by I t o h et a l . c o n s i s t e d of two  s u b s t r a t e , and  one  c o n t a c t s on the same s i d e of a SI  of the metal c o n t a c t was  separated  from the SI  substrate  w i t h a n - l a y e r , so t r a p s observed i n the paper by I t o h et a l . may originated  from the n - l a y e r , n - l a y e r - S I  substrate.  Over a l l ,  i n f o r m a t i o n on  i s v e r y l i m i t e d compared to other  s u b s t r a t e i n t e r f a c e or the  quoted papers on photocurrent-DLTS, except those  not been r e p o r t e d  T h i s may  the C r - r e l a t e d l e v e l HLI  i s the dominant l e v e l  c o u l d p o s s i b l e be compensated by HLI  3 .3  and  epitaxial  of the reasons why  EL2  photocurrent-DLTS, because  i n Cr-doped GaAs and  EL2  when a Cr-doped SI GaAs i s used.  B a s i c P r i n c i p l e s of Photocurrent-DLTS During  a light  which populate c u r r e n t due F i g . 3.2.  to emission During  fc  where n ( o ) ,  of c a r r i e r s from traps can be observed, as shown i n  T  can be w r i t t e n as  {n (0) fc  the o c c u p a t i o n  be d e s c r i b e d  A f t e r the l i g h t p u l s e , a t r a n s i e n t  the d u r a t i o n when the l i g h t i s o f f , the o c c u p a t i o n  n (t) =  t  e x c i t a t i o n p u l s e , e l e c t r o n - h o l e p a i r s are generated  t r a p s i n the sample.  trap with density N  can  above  by O l i v e r et a l . [30]  be one  f r e q u e n t l y i n SI GaAs u s i n g  GaAs  A l l the  Fairman e t a l [32] , were d e a l i n g w i t h e i t h e r Cr-doped SI GaAs or  has  SI  traps i n as-grown undoped SI LEC  types of GaAs s u b s t r a t e s .  l a y e r on top of Cr-doped SI GaAs.  have  n («)} t  of the  e x p  of a  [34]  {-(e + n  e ) t} + p  n.O)  t r a p j u s t when the l i g h t i s removed  by (under c o n d i t i o n of h i g h e x c i t a t i o n [7])  (3.4)  (t=0)  13  0  50 TIME  100 (ms)  F i g . 3 . 2 T r a n s i e n t c u r r e n t o b s e r v e d f o r sample 184-Cr a t 3 3 0 K. E x c i t a t i o n l i g h t p u l s e t u r n e d o f f a t t = 0 sec.  14  v + ^ } n n a  n (0)  = N {1  t  where a /a . and n p  T  v /v are the n p  thermal v e l o c i t y , steady  -  i  (3.5)  electron/hole capture  respectively.  n (°°),  n (») t  = N {1  the o c c u p a t i o n  t  s t a t e (t=°°) can be w r i t t e n  cross section, of the  and  t r a p a t dark,  as  + ^}  T  (3.6)  P  where e /e i s the e l e c t r o n / h o l e e m i s s i o n n p  rate constant.  I f one  f r e e - c a r r i e r d e n s i t i e s are n e g l i g i b l e (when compared to the c a r r i e r s ) i n the the l i g h t - o f f  sample when the l i g h t  c y c l e i s g i v e n by  i(t) =  the  emitted  i s o f f , the decay c u r r e n t i ( t ) d u r i n g  [20]  {e n (t) + n  assumes  t  e (N p  -  T  n ( t) }  (3.7)  t  where q i s the e l e c t r o n i c charge, w the a c t i v e t h i c k n e s s of the l a y e r from which the  c a r r i e r s are r e e m i t t e d  A f t e r s u b s t i t u t i n g Eq.  (3.4)  from t r a p s , and A the area of the  i n t o Eq.  (3.7), Eq.  (3.7)  becomes  - ( e +e i(t) = - ^ { ( e ^ e  )(n (0)+{n (0)-n (co)}e t  t  t  contact.  n  p  )t ) + N^,e  }  (3.8)  15  However, i n DLTS, one i s concerned s i g n a l d u r i n g the l i g h t - o f f c y c l e , related  to time w i l l  ( a f t e r combining  y t )  o n l y about  the change o f the  so any term i n Eq. (3.8) t h a t i s not  be s u b s t r a c t e d out and Eq. (3.8) can be r e - w r i t t e n as  with Eqs.  (3.5) and 3.6))  qWAN„ a v = -g-I {e - e H ( l + f i ) n n  -  n  1  e ~ " (1+^) p  1  } exp(-t/T)  (3.9)  where x = l / ( e + e ) i s d e f i n e d as the time c o n s t a n t o f the t r a p . n p r  trap a » a n p  For an e l e c t r o n  and e » e n p  ( s o t ~ l / e ) . Eq. (3.9) n '  reduces to  yt)  and  = ^N T-iexp(-t/T)  (3.10)  T  the output o f the boxcar averager ( A i ^ = ^ ( t ^ ) -  IpC^))  qWAN Aip  x-^expet^x)  - exp(-t /T)}  (3.11)  2  When the temperature T o f the sample i s v a r i e d , A i ^ a l s o v a r i e s because  T i s dependent on the temperature.  respect  to T, when  6Ai  which  with  SAip By s o l v i n g — r — - = 0, x (the value of x at 6T max  D  6T  A i ^ reaches a maxima,  =0.  the maxima o c c u r s ) i s found  to s a t i s f y  the f o l l o w i n g e q u a t i o n [12]  (1 - t,/x ) exp(-t_/x ) = (l-t./x ) exp(-t /x ) 1 max T. max 2 max 2 max r  This implies x max e  r v  can be obtained once t, and t 1  2  0  0  (3.12)  are s e t ( a s shown i n  16  F i g . 3.3). section  a  and  n  E -E L»  l  can  be determined from Eq.  (3.2)  as d e s c r i b e d  again  reduces to  in  3.1 For  (3.10) and  trap o^>>a^ and  a hole  (3.11) w i t h the  p»  e  e n  >  E c  l'  (3.9)  Eqs.  that T ~ l / e . A c c o r d i n g to Eq. P (3.11) , w i t h t < t , both e l e c t r o n and hole traps should induce p o s i t i v e 1  exception  2  peaks i n the DLTS spectrum ( i f the  assumption of a » x (a » a ) n p p n  e » e ^ ( e ^ » e ) for e l e c t r o n (hole)  t r a p s are v a l i d ) .  n  hole  n  and  e l e c t r o n t r a p s , the  Intrinsic light underneath the  from a 670  b i a s , the  captured  two  peak can  s p e c t r a obtained  dominant peak. s p e c t r a obtained  For  to the  from e l e c t r o n t r a p s .  are moved i n t o the bulk and  using  c a r r i e r s from hole  transient current.  then be r e s o l v e d these two  by comparing biases,  example, i f the peak has  by u s i n g  negative  would probably be caused by an  3.3  For a negative  bias applied  So  to  the  for  i n the DLTS spectrum would be m o s t l y  i n t h i s case, r e - e m i t t e d  the dominant c o n t r i b u t o r particular  used.  pairs just  by d i f f e r e n t e l e c t r o n t r a p s .  from c a r r i e r s r e - e m i t t e d  traps and  ( F i g . 3.5(b)) was  electron-hole  ( F i g . 3.4).  transient current  p o s i t i v e b i a s i s a p p l i e d , holes hole  creates  d i s t i n g u i s h between  e l e c t r o n s are moved from the a c t i v e r e g i o n underneath  gate i n t o the bulk and  contributed  nm LED  top metal contact  the e l e c t r o d e s ,  negative  s t r u c t u r e of 86-T  To  and  and  The  Similarly, i f a get  captured  t r a p s would  be  type of t r a p of a  the r e s p e c t i v e peak i n  a much higher  amplitude i n the peak  trap.  Experimental Procedures Specimens were f a b r i c a t e d using  pieces  the  d e t e r m i n i n g which i s the  b i a s than p o s i t i v e b i a s , then t h i s  electron  by  from four wafers from  four  different ingots.  The  four wafers were a l l undoped SI LEC  the <100> d i r e c t i o n ) from Cominco and 152-S67 and 184-S72. wafer was  cut w h i l e  r e s p e c t to e i t h e r  (The  first  GaAs (grown i n  they were l a b e l l e d 51-T128, 86-S37,  number s p e c i f i e s the i n g o t from which the  the second number s p e c i f i e s the wafer p o s i t i o n  the seed S or t a i l T of the i n g o t ) .  From the  data s u p p l i e d by Cominco, wafers 152-S67 and 184-S72 were deemed s t a b l e and 51-T128 t h e r m a l l y u n s t a b l e .  (Thermally  end  slices  are u n s t a b l e  from the t a i l  so the thermal  end  are s t a b l e w h i l e  stability  resistivity thermally  stable implies that  wafer does not l o s e i t s h i g h r e s i s t i v i t y d u r i n g h i g h temperature F o r i n g o t 86,  with  those  the  anneal).  from the  seed  s t a t u s of wafer 86-S37 i s not  certain. Fig.  3.5  experiment. of  shows the d i f f e r e n t  Cr Schottky  sample s t r u c t u r e s t h a t were used i n t h i s  p l a n a r pads ( F i g . 3.5(a)) were f a b r i c a t e d on  wafers 51-T128, 86-S37, 152-S67, and 184-S72 and  Cr, 152-Cr and 184-Cr, r e s p e c t i v e l y .  Cr Schottky  shown i n F i g . 3.5(b)) were f a b r i c a t e d on a thinned l a b e l l e d 86-T. of  The  p i e c e of t h i n n e d wafer was  as 51-Cr,  86-  pads (sandwich s t y l e  as  p i e c e of wafer 86-S37  and  obtained by g r i n d i n g a p i e c e  a s - r e c e i v e d wafer (~500um t h i c k ) i n a s i l i c o n c a r b i d e s l u r r y on a g l a s s  p l a t e f o l l o w e d by a chemical two  labelled  pieces  minutes.  e t c h i n a s o l u t i o n of 4H S0i  I n a d d i t i o n , two  2  Au-Ge ohmic p l a n a r pad  t  + 1H 0 2  + 1H 0 2  samples (having  2  for  the  same s t r u c t u r e as i n F i g . 3.5(a)) l a b e l l e d 63-T42 and 82-S14 that were used i n Lowe's work [33]  were a l s o b r i e f l y  f a b r i c a t i o n steps of the C r - S c h o t t k y in  s e c t i o n 4.34(iv)  ohmic sample.  while  looked  at i n t h i s experiment.  samples are the same as those  The described  s e c t i o n 4.34(v) d e s c r i b e s the steps f o r the Au-Ge  40|jm  (b) F i g * 3 - 5 Sample s t r u c t u r e s used experiment (a) P l a n a r s t r u c t u r e structure  i n photocurrent-DLTS (b) T h i n s a n d w i c h  21  The DLTS e x p e r i m e n t a l set-up was work.  This included  n o i s e and  developed d u r i n g the course of t h i s  improvement on e l e c t r i c a l  improvement on vacuum chamber and  shielding  thermocouple  to reduce system  external  f e a t u r e s to  i n c r e a s e the temperature measurement a c c u r a c y . A b l o c k diagram  of the e x p e r i m e n t a l set-up i s shown i n F i g . 3.6.  sample i s mounted i n s i d e a l i g h t probe  sample h o l d e r .  t h a t no wire bonding V i s established s u p p l y and generated  (A two  probe  sample h o l d e r was  nm  pulse generator.  light  V a r i a t i o n of temperature  o f the  supsample  to heat w i t h  by a c o p p e r - c o n s t a n t a n thermocouple. by a EG6G 181  light  e m i t t i n g diode w i t h b i a s  n i t r o g e n to c o o l and a power t r a n s i s t o r  the sample i s a m p l i f i e d  so  e l e c t r o d e s u s i n g an Anatek r e g u l a t e d power  by a HEMT 3300 GaAsP 670  the temperature monitored  two  A constant bias  the sample i s i l l u m i n a t e d w i t h r e p e t i t i v e p u l s e s of  i s done u s i n g l i q u i d  using a  designed and used  i s needed and much time can be saved).  between the two  p l i e d by an IEC F33  from  t i g h t vacuum chamber ( F i g . 3.7)  The  The c u r r e n t  current sensitive amplifier,  and  then fed i n t o a EG6G 165/162 d u a l gated i n t e g r a t o r - b o x c a r averager f o r s i g nal processing.  The  y-channel of a HP  the output of the boxcar v o l t a g e of the  3.4  7044A x-y  r e c o r d e r i s used  averager and the x-channel r e c o r d s the  to r e c o r d thermocouple  sample.  Results I n e a r l i e r work by Lowe [33], Au-Ge ohmic c o n t a c t samples (63-T42  82-S14) were used.  Except  the other papers mentioned  and  f o r M a r t i n e t a l . [23] and Rhee e t a l . [27] , a l l i n s e c t i o n 3.2  used  e i t h e r S c h o t t k y to ohmic  IEC  ANATEK  F33  MODEL  PULSE  25-20  GENERATOR  TEMPERATURE  "TRIGGER  Chamber-  r  sample  LED  PAR 165,162  HP 70AAA  BOXCAR  X-Y  AVERA GER  RECORDER  PAR 181 CURRENT AMPLIFIER Fig*  3.6  Block diagram  of photocurrent-DLTS  set-up  ro ro  LIQUID N CRYOSTICK 2  ELECTRICAL FEEDTHRQUGHS SAMPLE HOLDER LED  TO VACUUM PUMP  Fig.  3.7  Vacuum chamber used  i n the p h o t o c u r r e n t - D L T S  experiment  ro  **  1  f  I I  500 I  10  I  I  33 >  4  I  i  \  £  5  1  O  -n "0  X  cr cr ZD LU  U  0  30  (a)  LU  o  60  90  TEMPERATURE IC)  200  x:  or <  o 6i o tr 33 JO  m  JK  2  AO  CD rn  X  20  o 100 tz 33  m  0^-  30  (b)  60  90  TEMPERATURE (C)  Fig. 3.8 Graph o f temperature vs dark leakage c u r r e n t and r a t i o o f p n o t o c u r r e n t t o d a r k l e a k a g * c u r r e n t o f ( a ) S a m p l e 63T4-2 (b) Sample 51-Cr  25  d e v i c e s o r ohmic to ohmic d e v i c e s .  Rhee e t a l . used Au S c h o t t k y  d e v i c e s w h i l e M a r t i n e t a l . used Cr S c h o t t k y shown i n F i g . 3.5(b)) and r e f e r r e d complicated r e s u l t s " .  F i g u r e 3.8  to S c h o t t k y  to Schottky (same s t r u c t u r e as  to Au-Ge ohmic e l e c t r o d e s g i v i n g  shows the comparison between the dark  leakage o f a Au-Ge ohmic sample (63-T42) to t h a t o f a C r - S c h o t t k y (51-Cr).  "more  sample  The dark leakage c u r r e n t f o r 63-T42 r i s e s r a p i d l y once a tempera-  t u r e of 340K i s reached ( t h e r m a l l y generated)  and the assumption  of n e g l i g i b l e f r e e  taken i n Eq. (3.7) i s no l o n g e r v a l i d  i n t r o d u c e e r r o r to the photocurrent-DLTS scan, S c h o t t k y - S c h o t t k y  analysis.  carriers  and t h i s  So f o r h i g h  will  temperature  pads would be a b e t t e r c h o i c e to use than ohmic  pads. T y p i c a l photocurrent-DLTS  s p e c t r a , o b t a i n e d i n the temperature  range  220K t o 400K, o f samples 51-Cr, 86-Cr, 152-Cr, and 184-Cr are shown i n F i g s . 3.9 to 3.12, r e s p e c t i v e l y .  As the s p e c t r a show, a l l the samples r e v e a l e d  the same t h r e e t r a p s i n t h i s  temperature  range.  To determine  t r a p s a r e e l e c t r o n or h o l e types, sample 86-T was used. show spectrum  I t can be seen  i n the spectrum  higher  bias,  t h a t the peak h e i g h t s o f peaks TP1, TP2 and  o b t a i n e d u s i n g n e g a t i v e b i a s are a t l e a s t  than that o b t a i n e d u s i n g p o s i t i v e b i a s .  observed  these  F i g s . 3.13 and 3.14  f o r sample 86-T obtained using n e g a t i v e and p o s i t i v e  respectively. TP3  whether  peaks a r e due to e l e c t r o n t r a p s .  ten times  T h i s i n d i c a t e s t h a t these  I n t e r e s t i n g l y , both o f the  s p e c t r a o b t a i n e d u s i n g p o s i t i v e and n e g a t i v e b i a s on 86-T show a n e g a t i v e peak (AI<0) a t ~350K. a » a or e » e n p p n  I f a t r a p f o l l o w s the approximation  and o >>a p n  p h o t o c u r r e n t DLTS s p e c t r a .  that e » e and n p , then o n l y p o s i t i v e peaks should appear i n r  However, i f e  ~ e , then E q .  (3.11) i s no  ho  AI=2nA  TEMPERATURE Fig.  3.10  A photocurrent-DLTS  spectrum  (Kl  f o r sample  86-Cr  ( R a t e windowrMO  ms)  N3  00  AI=2nA  ro  TP3  TPA F i g . 3 . 1 3 A photocurrent-DLTS ( P o s i t i v e b i a s , r a t e window:20  spectrum ms)  f o r sample 8 6 - T  TEMPERATURE (Kl  TPA  F i g . 3.14 (Negative  A photocurrent-DLTS spectrum b i a s , r a t e w i n d o w : 2 0 ms)  f o r sample  86-T  T a b l e 3.1  Values of detected  and a c a l c u l a t e d  from F i g . 3.15  f o r the traps  by photocurrent-DLTS  Capture c r o s s s e c t i o n o  Label  E [eV]  API  0.80  4.9  X  AP2  0.72  1.3  X  10"  AP3  0.53  2.1  X  IO" *  BP1  0.80  1.9  X  IO **  BP2  0.72  3.4  X  IO"*  BP3  0.52  1.2  X  10"  CP1  0.76  1  X  10"  CP2  0.71  4  X  10"^  CP 3  0.53  7  X  10"  DPI  0.79  2.9  X  10"^  DP2  0.72  5.8  X  10"  DP3  0.50  2.9  X  io- *  TP 4  0.65  3  X  10"  T  i 2  2  -1  2  i 2  i k  2  i 3  A 2  3  i 5  (cm ) 2  n  EL12  EL2 AP13P1 CP1.DP1  EL3 TPA AF3.BP3  ELA  CR3,DF3  «//  CM  tt/o  O  0  51-Cr 86-Cr 152-Cr 18A-Cr 86-T  / t-/ A/*  2.5  3.5 1000/T  Fig.  // L/  3-15  Activation  energy  plot  4.5 I K" 1 1  for traps  detected  using  photcurrent-DLTS  CO CO  34  longer v a l i d  and n e g a t i v e peaks can o c c u r .  F o r a t r a p to have n e g a t i v e  peak, t h e c o n d i t i o n i(°°) - i ( 0 ) > 0 must be s a t i s f i e d . Eq. (3.8))  T h i s i m p l i e s (from  either a v  e  < e n p  and  e  < e  and  e < — v e  a  3.13(a)  or  p  n  e J l  e  <  p  a v P P  3.13(b)  a v n n  so f o r a trap w i t h an e l e c t r o n e m i s s i o n r a t e s m a l l e r than the h o l e  emission  r a t e w h i l e having an e l e c t r o n c a p t u r e c r o s s s e c t i o n g r e a t e r than the h o l e c a p t u r e c r o s s s e c t i o n , a n e g a t i v e peak would occur. rical  case a l s o g i v e s a n e g a t i v e peak.  Similarly,  the symmet-  Ogawa e t a l . [29] d e s c r i b e s t h i s as  being a t r a p i n t e r a c t i n g w i t h both bands. The  A r r h e n i u s p l o t s o f £ n T x v e r s u s 1/T f o r a l l the above 2  t r a p s are shown i n F i g . 3.15. l i n e s of t r a p s c l a s s i f e i d figure.  F o r comparison purpose,  observed  several signature  by M a r t i n et a l . [17] are a l s o shown i n the same  The v a l u e s o f the apparent  a c t i v a t i o n energy E^, and the c a p t u r e  c r o s s s e c t i o n s a were c a l c u l a t e d ( u s i n g E q . (3.2)) from the data i n F i g . 3.15 and are l i s t e d  The  i n T a b l e 3.1.  p o s s i b l e a s s o c i a t i o n o f observed  t r a p s can be summarized as f o l l o w s :  AP1,BP1,CP1,DP1  EL 2  AP2,BP2,CP2,DP2  EL12  35  AP3,BP3,CP3,DP3  EL4  TP4  0  r e l a t e d donor t r a p as  2  described [16]  In iated  t h i s experiment,  t r a p PI  w i t h the major donor l e v e l EL2.  dominant l e v e l ( S e c t i o n 2.3)  comparable w i t h and that the presence spectrum restricts observed  and  i n undoped SI LEC  observed  i n t h i s experiment  of a n e g a t i v e peak c l o s e by PI  by other a u t h o r s .  peak ( i d e n t i f i e d as TP4  EL12  and EL4  Both of these  The  i n undoped SI LEC  [32]  GaAs.  and  3  encapsulant  together w i t h EL2, LEC  GaAs.  i s a t most  reason c o u l d be  ( f o r example TP4)  t r a p s had been observed GaAs and EL4  i n Cr-doped Bridgman GaAs. a l s o observed  i n Bridgman GaAs and  i n the  The  and  by Lowe  had A  been  negative  by Fairman et  by O l i v e r e t a l .  [30]  O l i v e r et a l . b e l i e v e t h i s n e g a t i v e peak i s an  o x y g e n - r e l a t e d l e v e l w i t h oxygen coming from the wet 2  semi-  have not been f r e q u e n t l y  i n t h i s experiment) was  i n Cr-doped SI LEC  lOOOppm) B 0  GaAs i s assoc-  the s u p e r p o s i t i o n of PI w i t h the n e g a t i v e peak reduces  the peak h e i g h t of P I .  [15]  i s sometimes d e s c r i b e d as the  i n p r e v i o u s study at U.B.C. on undoped SI LEC  [32]  and Ogawa et a l .  not dominant over o t h e r l e v e l s .  i d e n t i f i e d by Fairman e t a l .  al.  EL2  et a l .  i n V.P.E. and bulk ( b o t h c o n d u c t i v e and  i n s u l a t i n g ) m a t e r i a l , however, PI  [33]  observed  in Oliver  ( h i g h water content  l a y e r d u r i n g c r y s t a l growth and  that t h i s  i s r e s p o n s i b l e f o r the compensation e f f e c t  e f f e c t of water content of the B 0  a l s o i n v e s t i g a t e d by Rumsby e t a l . [35] , and  2  3  level,  i n undoped SI  l a y e r on LEC  they observed  ~  GaAs  that high  was  36  resistivity  c r y s t a l s were o b t a i n e d when a wet  B 0  3  l a y e r was  resistivity  c r y s t a l s were obtained w i t h a dry B 0  3  layer.  2  2  water content i n B 0 2  may  3  used w h i l e  low  T h e r e f o r e , the  have some e f f e c t on the compensation mechanism i n  LEC GaAs as O l i v i e r e t a l [30]  proposed  and  the n e g a t i v e peak (TP4)  observed  0  in  the photocurrent-DLTS  s p e c t r a may  be the r e s u l t of the water content i n  B 0 . 2  3  The  r e l a t i v e h e i g h t s of the peaks f o r P1(EL2) and P2(EL12) f o r  samples from d i f f e r e n t believed  s l i c e s are compared i n T a b l e 3.2.  to be t h e r m a l l y u n s t a b l e , has  the lowest r a t i o of PI  compared to the other samples which are e i t h e r d e f i n i t e l y t h e r m a l l y s t a b l e (152-Cr and 184-Cr) or h a l f way s l i c e s and u n s t a b l e s l i c e s t h a t f o r undoped SI LEC  (86-Cr).  GaAs, thermal  and w i t h EL2  sample 51-Cr, to P2 when  indicated  to be  on the i n g o t between s t a b l e  I t has been shown by Ta et a l . [36] stability  w i t h s t o i c h i o m e t r i c or A s - r i c h c o m p o s i t i o n . P1(EL2),  The  b e l i e v e d to be a As  i s achieved o n l y f o r samples  Having  low c o n c e n t r a t i o n of  complex, sample 51-Cr  is  Ga expected  to have high Ga/As melt  thermally unstable.  c o m p o s i t i o n d u r i n g growth and t h e r e f o r e  S i m i l a r l y , f o r 86-Cr, the Ga/As melt c o m p o s i t i o n must  have changed from h i g h i n the seed end of the i n g o t to low i n the t a i l The  above r e s u l t i s v e r y i n t e r e s t i n g  stability  because i t i m p l i e s t h a t the  end.  thermal  of a GaAs i n g o t can be a s c e r t a i n e d not o n l y by measuring  resistivity  b e f o r e and  a f t e r h i g h temperature  r e l a t i v e peak h e i g h t s of a photocurrent-DLTS  anneal  but a l s o by  spectrum.  comparing  37  T a b l e 3.2  R e l a t i v e peak h e i g h t of PI to P2  R e l a t i v e peak h e i g h t of PI to P2 (x .= 40ms)  Sample  Average r e l a t i v e peak h e i g h t of PI/P2 ( o v e r 5 scans)  51-Cr  0.18  0.21  86-Cr  0.97  0.98  152-Cr  2.0  2.25  184-Cr  0.79  0.81  To summarize, the f o l l o w i n g c o n c l u s i o n s can be made: (1)  T h r e e e l e c t r o n l e v e l s were found  different  i n g o t s , s u p p l i e d by Cominco.  i n a l l four s l i c e s , from f o u r The r e s u l t  suggests  l e v e l s a r e c h a r a c t e r i s t i c s of GaAs wafers from Cominco. e n e r g i e s o f these l e v e l s were found  that these  three  The a c t i v a t i o n  to be 0.80, 0.72, 0.52 eV and they  were  a s s o c i a t e d w i t h e l e c t r o n l e v e l s EL2, EL12 and EL4, r e s p e c t i v e l y . (2)  A negative  peak that was observed  was a l s o d e t e c t e d al.  shallow  i n undoped SI LEC GaAs.  Thermally  s t a b l e s l i c e s were shown to have h i g h e r r e l a t i v e peak h e i g h t  r a t i o of P i (0.80 eV) to P2 (0.72 eV) than t h a t i n t h e r m a l l y slices.  [30,32]  T h i s l e v e l i s b e l i e v e d , by O l i v e r et  [ 3 0 ] , t o be r e s p o n s i b l e , together with EL2, f o r compensating  acceptors (3)  i n t h i s experiment.  p r e v i o u s l y by other authors  unstable  Hence, t h e r m a l l y u n s t a b i l i t y could have been caused by under  compensation due to the lower c o n c e n t r a t i o n of E L 2 .  38  CHAPTER 4 DISLOCATIONS AND DEVICE CHARACTERISTICS  4.1  Introduction  L a r g e diameter (50-75mm) LEC GaAs s l i c e s g e n e r a l l y have a high d i s l o c a t i o n density (10 -10 cm" ). 4  nominally  5  dislocation free.  2  By c o n t r a s t C z o c h r a l s k i - S i i s nowadays  As the demand f o r GaAs i n high speed IC  a p p l i c a t i o n i n c r e a s e s , the q u e s t i o n of the e f f e c t o f d i s l o c a t i o n s on d e v i c e c h a r a c t e r i s t i c s becomes  important.  D i s l o c a t i o n s have been known f o r some time to have harmful e f f e c t s on l i g h t - e m i t t i n g diodes t i o n regions  [37],  and l a s e r s i n which they cause n o n r a d i a t i v e  recombina-  F o r GaAs MESFET, the p o s s i b l e e f f e c t s o f d i s l o c a t i o n s on  device c h a r a c t e r i s t i c s ,  i n p a r t i c u l a r on t h r e s h o l d v o l t a g e , are c r u c i a l to  the development o f l a r g e s c a l e IC.  Published  work i s not i n agreement on  the i n f l u e n c e o f these d e f e c t s on t h r e s h o l d v o l t a g e . p u b l i s h e d work i s presented  A b r i e f review o f  i n s e c t i o n 4.2.  A primary cause o f d i s l o c a t i o n s i n GaAs i s b e l i e v e d to be t h e r m a l l y induced  s t r e s s o r i g i n a t i n g from a x i a l and r a d i a l  i n g c r y s t a l growth [ 3 8 ] . can be obtained [39]  temperature g r a d i e n t s dui>-  D i s l o c a t i o n d e n s i t i e s and t h e i r v a r i a t i o n s i n GaAs  from the e t c h p i t d e n s i t i e s (EPD) u s i n g a molten KOH  or a A-B e t c h  [40].  EPD v a r i a t i o n a c r o s s  etch  F o r l a r g e diameter (50-75mm) undoped SI LEC GaAs,  the diameter g e n e r a l l y f o l l o w s a W p a t t e r n f o r wafers  near the seed end o f an i n g o t and i t c o u l d e i t h e r f o l l o w a W p a t t e r n or a U p a t t e r n f o r wafers near the t a i l  end of an i n g o t ( f o r example, see Ref. 4 1 ) .  39  On  a microscopic  s c a l e , the d i s l o c a t i o n s form a honeycomb-like network of  c e l l s w i t h diameter of the c e l l s ranging to EPD  o f approximately  lxl0 cm" ). 5  t h i s network takes on a new lines (Fig.  4.1).  from 100um to 500jjm  When the EPD  2  i s l e s s than  s t r u c t u r e where the e t c h p i t s  Chen et a l . [41]  reported  (corresponding 2xl0 cnF , 1 +  2  form v i s i b l e wavy  that these d i s l o c a t i o n  net-  works were formed to minimize the s t r a i n energy, of the GaAs c r y s t a l . To  have a c o n d u c t i v e  experiment) should order  n-channel, the implanted  s e t t l e on a Ga  to a c t as an n-type dopant.  s i t e during  ions.  Heinke and  annealing  in  vacancies Queissen  have shown that d i s l o c a t i o n s i n GaAs a c t as a s i n k of nearby d e f e c t s i n  which d e f e c t s surrounding core. any  post-implantation  Thus the c o n c e n t r a t i o n of Ga  a f f e c t s the amount of a c t i v a t i o n of implanted [42]  ions ( S i i n t h i s  Whether or not  a d i s l o c a t i o n are g e t t e r e d i n t o the  t h i s k i n d of d e f e c t g e t t e r i n g around a d i s l o c a t i o n  e f f e c t on the a c t i v a t i o n e f f i c i e n c y of implanted  threshold voltage  dislocation  is s t i l l  not c l e a r .  I n the present  i o n s and  has  hence the  work, MESFET were  f a b r i c a t e d on an undoped SlO.00^LEC GaAs sample, u s i n g f a c i l i t i e s a v a i l a b l e a t U.B.C, and respect  4 .2  the s c a t t e r of d e v i c e c h a r a c t e r i s t i c s was  to the d i s l o c a t i o n d i s t r i b u t i o n on the same sample.  B r i e f Review of P u b l i s h e d Work S e v e r a l papers d i s c u s s e d  LEC  i n v e s t i g a t e d with  GaAs c r y s t a l .  reported  The  e f f e c t of ambient gas  by Emori et a l . [ 4 3 ] .  when krypton  was  the e f f e c t of c r y s t a l growth parameters on undoped LEC  GaAs  on  was  D i s l o c a t i o n d e n s i t i e s were found to decrease  used i n s t e a d of argon, n i t r o g e n or helium.  Ta e t a l .  [44]  (b) F i g . 4.1 E t c h p i t s t r u c t u r e i n sample 283-S11 showing (a) honeycomb-like network and ( b ) w a v y l i n e s  41  and Holmes e t a l . [45] found that SI GaAs p u l l e d r i c h melts showed e x c e l l e n t materials exhibited  cm . -2  low ambient  Improved LEC  i n an attempt  to heat treatment w h i l e SI G a - r i c h  p-type c o n v e r s i o n .  good diameter c o n t r o l , m e l t s and  stability  thick B 0 2  from s t o i c h i o m e t r i c or As-  Chen et a l . [41] showed the use of  encapsulating layers,  3  slightly  As-rich  p r e s s u r e gave d i s l o c a t i o n d e n s i t i e s as low as 6000  techniques have been d e s c r i b e d  i n the past s e v e r a l years  to o b t a i n low and homogeneous d i s l o c a t i o n d e n s i t y GaAs.  a p p l y i n g a v e r t i c a l magnetic  field  By  to the GaAs melt, Terashima e t a l . [46]  and Osaka et a l . [47] showed that temperature  f l u c t u a t i o n s i n the melt were  g r e a t l y reduced and t h e r e f o r e , more homogeneous c r y s t a l s can be o b t a i n e d . a c h i e v e a low temperature g r a d i e n t around [48,49] developed a new LEC by h e a t i n g the B 0 2  3  the growing  a d i s l o c a t i o n d e n s i t y o f 1000cm  was  -2  was  increased  Using t h i s technique,  observed by Shimada e t a l . i n 2 - i n -  N e a r l y d i s l o c a t i o n - f r e e GaAs (20-35 mm  r e p o r t e d by Jacob et a l . [50] when the c r y s t a l was  indium or antimony.  I t i s believed  gradient  through a window on the s u s c e p t o r w a l l  and by s e t t i n g up a thermal b a f f l e above the c r u c i b l e .  diameter undoped SI GaAs.  c r y s t a l , Shimada et a l .  technique which reduced the temperature  encapsulant layer  To  diameter)  h e a v i l y doped w i t h  [50,67] that the a d d i t i o n of I n or Sb  the r e s i s t a n c e of the c r y s t a l  to the g e n e r a t i o n and p r o p a g a t i o n of  d i s l o c a t i o n s d u r i n g growth. The  r e l a t i o n s h i p between EL2  c o n c e n t r a t i o n d i s t r i b u t i o n and  disloca-  t i o n d i s t r i b u t i o n i n a GaAs wafer have been s t u d i e d by a number o f a u t h o r s . Holmes et a l . [51] r e p o r t e d the p a t t e r n of EL2 d e n s i t y a c r o s s the wafers GaAs i n g o t s was  toward  c o n c e n t r a t i o n and  dislocation  the seed end of 3 - i n - d i a m e t e r SI<100>LEC  the same ( t h a t i s , they both have a W-shaped p a t t e r n a c r o s s  42  the w a f e r ) . along  T h i s r e l a t i o n was not observed f o r wafers near the t a i l  the i n g o t .  end or  M a r t i n e t a l . [52] observed that EL2 c o n c e n t r a t i o n and  d i s l o c a t i o n d e n s i t y had the same p a t t e r n across wafers but not along the ingot.  Both Holmes e t a l . and M a r t i n e t a l . d i d not c l a i m  direct  q u a n t i t a t i v e c o r r e l a t i o n between EL2 c o n c e n t r a t i o n and d i s l o c a t i o n Brozet e t a l . spatial  [53] r e p o r t e d  density.  s i m i l a r r e s u l t s as t h a t above by u s i n g  r e s o l u t i o n near i n f r a r e d  absorption.  high  I n a d d i t i o n , they observed  s t r u c t u r e superimposed on to the EL2 c o n c e n t r a t i o n v a r i a t i o n and t h i s s t r u c t u r e can be r e l a t e d to g e t t e r i n g of EL2 ( o r d e f e c t s ) cores.  2xl0 cm~ . 5  2  fine  to d i s l o c a t i o n  Hasegawa e t a l . [19] r e p o r t e d good c o r r e l a t i o n on undoped  n-type LEC GaAs, both seed end and t a i l  conductive  end, f o r wafers w i t h EPD h i g h e r  However, with EPD l e s s than 2 x l 0 c m 5  - 2  fine  than  , Hasegawa e t a l . r e p o r t e d  t h a t the EL2 d e n s i t y was almost independent of the EPD.  For Martin  et a l . ,  Holmes e t a l . , and B r o z e l e t a l . the c o n c e n t r a t i o n of EL2 was determined by near i n f r a r e d  o p t i c a l a b s o r p t i o n while  was determined u s i n g c a p a c i t a n c e The SK10OLEC and  f o r Hawegawa e t a l . , EL2  concentration  DLTS.  e f f e c t of d i s l o c a t i o n on leakage c u r r e n t a c r o s s wafers of undoped GaAs was s t u d i e d by Miyazawa e t a l . [ 5 4 ] , Matsumura e t a l . [ 5 5 ] ,  Matusmoto et a l . [ 5 6 ] . I t was found that f o r wafers near the seed end,  the leakage c u r r e n t was i n v e r s e l y p r o p o r t i o n a l to e t c h p i t d e n s i t y .  Further-  more, Matsumoto e t a l . d i d not observe t h i s c o r r e l a t i o n between d i s l o c a t i o n d e n s i t y and leakage c u r r e n t h i g h temperature anneal  f o r wafers near the t a i l  end and found t h a t a  s i g n i f i c a n t l y smooths out the inhomogeneity of  leakage c u r r e n t a c r o s s a wafer. r e s i s t i v i t y was a l s o looked  The d i s l o c a t i o n e f f e c t on H a l l m o b i l i t y and  at [55,57,58] and H a l l m o b i l i t y was shown to be  43  proportional  to the  proportional  to EPD.  l o g a r i t h m of the EPD The  e l e c t r i c a l homogeneity of the  undoped SI<100>LEC GaAs was resistance  and  ted w i t h the  w h i l e r e s i s t i v i t y was  investigated  S i implanted l a y e r  by Honda et a l . [59],  sheet c a r r i e r c o n c e n t r a t i o n were found to be  d i s l o c a t i o n density  distribution.  was  d i r e c t l y proportional  to that  the  reported  of sheet  in  both sheet  closely  C o n t r a r y to  r e p o r t e d by Matsumura et a l . [55] , B l u n t et a l . [60] l o c a t i o n density  inversely  correla-  result  that  the  dis-  resistance.  However, B l u n t et a l . used Cr-doped SI<001>LEC GaAs w h i l e Matsumura e t a l . used undoped SI<L00>LEC GaAs. The  q u e s t i o n of whether d i s l o c a t i o n s  MESFET performance has  been s t u d i e d  by  SI<100>LEC GaAs, Nanish et a l . [61] area showed h i g h d r a i n  have any  several  reported  source c u r r e n t  deleterious  groups r e c e n t l y .  that FET and  effects  low  For  fabricated  threshold  undoped  on h i g h  v o l t a g e (V  DS as compared to those on  low EPD  doped SK100XLEC GaAs was undoped case. the V the  (fabricated  d i s t a n c e between the FET  the  ^  w  a  s  The  v a r i a t i o n of I  shown [65]  on Cr doped SK100XLEC GaAs) was and  d i s l o c a t i o n density.  affected  the  by  MESFET a l s o  threshold the  than when they were near the hand, no  central  p a r t s of  pit).  v o l t a g e standard  lower  deviation  and  d i s l o c a t i o n network c e l l w a l l .  not  higher V , th  the d i s l o c a t i o n c e l l  d i r e c t evidence of d i s l o c a t i o n e f f e c t s on V  on  MESFET  network and  DS i n the  that  lower V , than those f a r th  dislocation cell  exhibited  ,) tn  the  dependent  nearest d i s l o c a t i o n ( e t c h  J  when they were l o c a t e d  in  EPD  Cr-  by Miyazaiwa et a l . [63,64] r e p o r t e d  Furthermore, the to be  across a  to have s i m i l a r r e s u l t s as  l e s s than 50um from a d i s l o c a t i o n e x h i b i t e d  from a d i s l o c a t i o n . oV  shown [62]  Recent p u b l i c a t i o n s  of a FET  located  area.  on  On  the  were observed  network other [66]  44  f o r MESFET on Cr-doped SI<1L1>HB GaAs; but i n t h i s case, n o n u n i f o r m i t y V  of  between wafers from d i f f e r e n c e i n g o t s was a more s e r i o u s problem.  F i n a l l y , a r e c e n t paper by Winston e t a l . [67] r e p o r t e d result  to t h a t of Miyazawa e t a l . [63,64].  a contradictory  Winston e t a l .  observed no  c o r r e l a t i o n between a t r a n s i s t o r ' s V , and i t s d i s t a n c e to a n e a r e s t th d i s l o c a t i o n f o r e i t h e r I n - a l l o y e d LED GaAs (IN„ n ^ G a - QQ-TAS) o r u.uuJ  u•yy/  c o n v e n t i o n a l LEC GaAs and t h a t the V , was more uniform th  on l o w - d i s l o c a t i o n  I n - a l l o y e d LEC GaAs than on h i g h e r - d i s l o c a t i o n c o n v e n t i o n a l LEC GaAs.  4.3  D e s c r i p t i o n of Mask and D e v i c e F a b r i c a t i o n An a r r a y of t e s t i n g d e v i c e s was designed  a r r a y was made.  The r u b y l i t h was sent  f o r f a b r i c a t i o n of the photographic repeated  to f i l l  d r a i n source  to P r e c i s i o n Photomask L t d . of Quebec  mask.  the mask (2.5inx2.5 i n ) .  o f MESFET and an a r r a y of Schottky  and a r u b y l i t h copy of the  The d e v i c e a r r a y was stepped and The d e s i g n c o n s i s t e d o f an a r r a y  pads; gate l e n g t h , channel width and  d i s t a n c e of these MESFET were 4 pm, 25pm, and 10urn,  respectively.  A gate l e n g t h of 4pm was used to assure  dimension of 50pmxl00pm  high y i e l d .  was used f o r the gate and d r a i n and source  pads so that there i s enough room to manipulate the probes i n a s t a t i o n to c o n t a c t other.  the a p p r o p r i a t e  pads without  pad was 140pmxl20pm  contact  multi-probe  the probes s h o r t i n g each  The s e p a r a t i o n between the gate of two adjacent  dimension f o r the Schottky  A  FET was 110 pm.  The  w i t h a s e p a r a t i o n of 10pm  between pads. S i x p a t t e r n s were designed multiple direct  f o r use i n f a b r i c a t i n g  the a r r a y  s e l e c t i v e i o n i m p l a n t a t i o n as the p r o c e s s .  with  The r e q u i r e d s i x  p a t t e r n s were grouped i n t o a s i n g l e mask ( a s shown i n F i g . 4.2) to save  45  (F)  (E)  (D)  (o TJuiriJTJTTiriTLTTrTrTTiJtrTr^TrTrirTJTr  (B)  ImiJTfTfLT^  (A)  200jJm Fig.  4.2  Mask f o r d e v i c e  array  46  money.  From F i g . 4.2,  p a t t e r n A i s the r e g i s t r a t i o n marks, p a t t e r n B i s the  n-implant, p a t t e r n C i s the n  +  implant  and  ohmic c o n t a c t s , p a t t e r n D i s the  gate m e t a l l i z a t i o n , p a t t e r n E i s the Schottky metal c o n n e c t i o n  pads, and  p a t t e r n F i s the  t h a t c o u l d be used to connect an a r r a y of FET  together  for  future surface analysis studies.  4.3.1  Substrate  Preparation  A p i e c e of wafer (1.5cmxO.9cm) was  cut from an undoped SI<100>LEC  GaAs s l i c e ( l a b e l l e d 283-S11) from Cominco. following  p r e c l e a n i n g procedure ( p r o v i d e d  F a b r i c a t i o n began w i t h  to t h i s group by Mr.  the  G. Needham of  Cominco): i)  A  two  and ii)  p a r t degreasing  c o n s i s t i n g of a 5 minute b o i l i n g  a 5 minute b o i l i n g i s o p r o p a n o l  acetone bath  bath.  A GaAs e t c h c o n s i s t i n g of a 4 minute immersion i n a f i l t e r e d ALCONOX (Monosodium dihydrogen phosphate) s o l u t i o n at 25 °C followed  iii)  An  by a 15  second r i n s e i n DI  oxide e t c h c o n s i s t i n g of a 30  1H 0 :1NH 0H:240H 0 and 2  iv)  2  1+  2  and  water.  second immersion i n by a 15  second r i n s e i n DI  water.  A f i n a l b o i l i n g i s o p r o p a n o l bath f o r 2 minutes, the wafer then b e i n g immediately put  4.3.2  followed  1%  Ion An  i n t o the Plasma-Therm system f o r SigN^ d e p o s i t i o n .  Implantation SijN^ film  of 900A t h i c k n e s s was  deposited  on the wafer by plasma-  e n c h a n c e d - c h e m i c a l - v a p o u r - d e p o s i t i o n (PECVD) technique Therm HFS  500E RF  system ( F i g . 4.3a).  The  using  the Plasma-  t h i c k n e s s of the f i l m  measured by an e l l i p s o m e t e r c o n t r o l l e d by PDP8e.  was  T h i s Si3N4 f i l m would  47  remain throughout of  the process so as to p r o t e c t the GaAs s u r f a c e .  the Plasma-Therm system f o r the d e p o s i t i o n are shown i n T a b l e 4.1.  T a b l e 4.1  Settings for Si N. film 3  NH  3  d e p o s i t i o n by PECVD  flow r a t e  75 SCCM  He flow r a t e  500  SCCM  5% S N /He  500  SCCM  Pressure  1525  Temp, of S u b s t r a t e  308 °C  R.F.  100 W  3  4  Power  D e p o s i t i o n Time  The  f i l m was then annealed  liter/minute) of  the f i l m was observed 3  The S i N 3  l +  +  film  6 min.  heat  tube f u r n a c e . treatment.  f o r n-implant  acetone  2  (1  No evidence o f c r a c k i n g  I n the next  s t e p , windows  w i t h the f o l l o w i n g procedure.  f i l m was cleaned by a 5 minute b o i l i n g  a 5 minute b o i l i n g bath.  after  um  a t 850°C f o r 14.5 minutes i n f l o w i n g N  i n a M i n i Brute s i l i c a  were opened i n the Si N,  i)  Settings  trichloethylene  bath and a 5 minute b o i l i n g  bath,  TRANSENE 100  The wafer was then put i n t o a Statham SD6 oven at 200°C f o r 30  minutes to e l i m i n a t e water content on top o f f i l m .  48  ii)  S h i p l e y AZ1450J p h o t o r e s i s t was at 100°C i n the Statham SD6 aligned  deposited  onto the SigN^ f i l m ,  oven f o r 25 minutes, wafer was  to a p p r o p r i a t e mask and exposure to UV  light  baked  then  f o r 30  seconds  u s i n g a Kasper mask a l i g n e r , f o l l o w e d by a 2 minute p h o t o r e s i s t development iii)  and then a DI water r i n s e ( F i g . 4.3  b) .  E t c h i n g of SigN^ through windows f o r 9 minutes ( a t an e t c h r a t e of 50A/min) i n b u f f e r e d HF reduced the t h i c k n e s s of S i N i 3  t  f i l m under the  windows by 450A ( F i g . 4.3C). iv)  A S i implant  was done to produce an n - l a y e r with an energy of 120  and a dose of 3.38x10 cm~ i2  implanter.  2  using the U.B.C. E x t r i o n 200  Removal of the p h o t o r e s i s t a f t e r implant  oxygen a s h i n g  i n the Plasma-Therm system.  T a b l e 4.2  Ion  was done by shows the  s e t t i n g s t h a t were used ( F i g . 4.3d)  T a b l e 4.2  S e t t i n g s f o r oxygen ashing u s i n g Plasma-Therm  0  2  flow r a t e  pressure Temp, of R.F.  200 SCCM 250  Substrate  power  Ashing time  um  120° C 200 25  W minutes  kev  49  v)  Step ( i ) , ( i i ) and ( i v ) were repeated again f o r the n  +  this  i 3  case, an energy  of 100  eV  implant.  and a dose of 3 . 3 7 x l O c m  - 3  In  were used  ( F i g . 4.3e) .  4.3.3  Post-implant Following  sputtering 4.3f).  implantation, a S i 0  i n a P e r k i n - E l m e r 3140  A n n e a l i n g was  in flowing N  2  RF  2  l a y e r 0.1um  t h i c k was  d e p o s i t e d (by RF  system) to serve as an anneal cap ( F i g .  done i n a M i n i Brute f u r n a c e at 850°C f o r 20  (1 l i t e r / m i n u t e ) .  minute b u f f e r e d HF  4.3.4  anneal  The  Si0  2  f i l m was  minutes  then removed by a 1  etch.  Metallization Ohmic c o n t a c t s of N i on top of AuGe (88% Au,  12% Ge)  were put down  u s i n g the f o l l o w i n g procedure. i)  Windows f o r the ohmic c o n t a c t s were opened by r e p e a t i n g step ( i ) , ( i i ) and ( i i i ) of s e c t i o n 4.3.2  ii)  P h o t o r e s i s t was s e c t i o n 4.3.2  ( F i g . 4.3g).  then removed by acetone  were repeated  soak i n room temperature the ohmic c o n t a c t window.  step ( i ) and ( i i ) of  together w i t h a 2 minutes  chlorobenzene  b e f o r e p h o t o r e s i s t development to r e - d e f i n e T h i s step i s necessary because w h i l e doing  a SigN^ e t c h , the b u f f e r e d HF original  and  a l s o weakens the p h o t o r e s i s t and  l a y e r of p h o t o r e s i s t i s then no l o n g e r able to l i f t  heavy l a y e r of Au-Ge/Ni.  The  chorobenzene soak i s used  the top l a y e r o f the p h o t o r e s i s t to the developer  the  o f f the  to s t r e n g t h e n  so t h a t an  undercut  50  edge p r o f i l e can be obtained upon p h o t o r e s i s t development and l i f t - o f f of iii)  metal l a t e r would be e a s i e r ( F i g . 4.3h).  E l e c t r o n beam e v a p o r a t i o n o f AuGe/Ni to a t o t a l  t h i c k n e s s o f 2000A  u s i n g Veeco VE 400 ( F i g . 4 . 3 i ) . iv)  Liftoff  o f unnecessary  metal  c o n t a c t s were then a l l o y e d heated v)  by immersion i n 1112 remover and ohmic  f o r 10 minutes i n a M i n i Brute f u r n a c e pre-  to 450°C w i t h f l o w i n g N  2  ( F i g . 4.3j) .  Gate m e t a l l i z a t i o n was done by r e p e a t i n g step ( i ) , ( i i ) and ( i i i ) of this section. of  The l i f t o f f  procedure  was then performed  after a layer  2000A t h i c k of A l was d e p o s i t e d ( F i g . 4.3k,l) .  To o b t a i n a r r a y s of S c h o t t k y pads, step (v) o f t h i s s e c t i o n , with Cr as the m e t a l , was r e p e a t e d .  4.4  Measurements After  the MESFET was made, the d r a i n - s o u r c e c u r r e n t ( I  d r a i n - s o u r c e v o l t a g e (V  n c  ) versus  ) c h a r a c t e r i s t i c s were s t u d i e d u s i n g a T e k t r o n i x  Do  577  curve t r a c e r w i t h c o n n e c t i o n to the FET made under a m u l t i - m a n i p u l a t o r  probing system.  I v e r s u s gate v o l t a g e (V ) c h a r a c t e r i s t i c s DS GS  MESFET were then measured.  f o r every  I n t h i s measurement, the wafer was put i n s i d e  the probing system w i t h the MESFET under study p r o p e r l y connected. V  o f 2V (from an Anatek r e g u l a t e d power supply model 25-20) was a p p l i e d to  the d r a i n ohmic pad w h i l e the output 181  A fixed  current amplifier.  A V  of the source pad was taken to an EG&G  of 2V was used  so as to assure that the MESFET  U b  was o p e r a t i n g i n the s a t u r a t i o n r e g i o n .  The two a d j a c e n t FET t o the FET  under study were pinched o f f by the a p p l i c a t i o n o f -1.5V to t h e i r gate so  51  / / / / / / / / / //SiaN / A  SI (a)  Si N 3  A  //IIIIIII!  GaAs  deposition  \\ \\\ I I I I 1 I I I I /Si.^//  SI  >  \  \  R  E  S  I  S  T  ^  ^  \  /////////  GaAs  (b) photoresist development  \\  \ \ / h / i/ I/ l\/  \ \ RESIST. \T I , i , . r, , , i / / S i N A / / / l  SI  3  GaAs  (c) Si^N etch for implant A  w  \ \ / / / / / / / / / / ' / / '3 4 / / / n - _LAYER \  \  R  E  S  S  I  S  T  \  N  SI GaAs (d)  channel  implant  F i g . 4.3 Fabrication MESFET a r r a y  sequence  for  the  \  \  52  \ \  \\\  \\\ T  (e)  I  +  n* implant  i  \\)\  n  i  A \RESIST\W  , , , '/ / S i g N / / / A  1  n+  SI GoAs  5i0 ! n  ~r~r "1 i i  n  1i  1  _* n  2  r i  SI GaAs  (f ) encapsulation and a n n e a l  113? I  \ \RESIST\\ \ / /S i3 N / / /  \\\ i  i  n  I  t  A  J._ ...j  n  n  +  SI  +  GaAs  ( g ) resist development for Si3N^ e t c h  chloro benzene modified layer  1  77^  1A  WRESISTW \ //SiaNA / / /  \ \\  / +  i i  n  i  / i  n  +  1  L_ _.i n  1  !  n  1  j J  SI GaAs ( h ) resist development for ohmic metallization Fig.  4.3  c o n t ' d  53 •  •  i r •  i l l  TT  •  \ \  •  •  •  \\\  ///  I  •  •  •  1 •  *  *  n  •  •  *  •  •  •  \W > j/ / / • 1  9 9 9  •  +  *  n  J  •  :: METAL: :: URESISTW .| //Si^// /  » 1  +  SI GaAs  ( i) source-drain metallization  77>r/W]rTTTTl 1 7 ^ !  n  +  ! i  SI (j)  n  ! !  n  GaAs  removal of resist (lift-off)  T^/I I l\n~TTTT\ !  n  \ \ \ \ \ \ \ RESISTv \ \  i  \\Trrr\Aiis\^ i  i n  n  11  L  +  SI GaAs ( k) resist development for gate metallization  &8I  1::::  HWIII  n  i _ _ _ • n  SI  4.3  cont'd  _  n*  GaAs  ( I) gate metallization Fig.  ::::!  i i  / /Si N 3  A  / //  54  i s o l a t i o n of the FET from zero p l o t was plot  can be o b t a i n e d .  a t zero gate b i a s and  as the gate v o l t a g e at which an I  e t c h , the  a b i a s of 6V  sample was  top of the  put  First,  recorder.  and  D  -V  GS  From each author  Cr-Schottky  the dark leakage c u r r e n t  was  A f t e r a l l the measurements, etch.  then put  I n the  sample was  dislocation  beads were then  i n s i d e an oven, a f t e r taken out,  put an  c o o l e d down, and  A f t e r the d i s l o c a t i o n e t c h , s e v e r a l measurements were  the d i s t a n c e between each MESFET and  recorded;" then the l o c a l  the n e a r e s t  e t c h p i t were  e t c h p i t d e n s i t y i n a 200umx200um area centered  each MESFET were c o l l e c t e d ; the whole sample were  An I  i s observed) were  i n s i d e a n i c k e l c r u c i b l e , KOH  sample, the c r u c i b l e was  r i n s e d with DI water.  finally,  at  the d i s l o c a t i o n network s t r u c t u r e over  recorded.  Results On  FET  of 2uA  sent to Cominco f o r a molten KOH  e t c h time of 5 minutes at 500°C, the  4.5  Do  u s i n g the EG&G181 c u r r e n t a m p l i f i e r .  the sample was  then v a r i e d  the dark leakage c u r r e n t between adjacent  pads were measured by a p p l y i n g recorded  was  the t h r e s h o l d v o l t a g e (which the  Do  Finally,  GS  can be observed.  Do  made f o r each MESFET u s i n g the HP7044A X-Y  resolved.  made:  gate b i a s V  to a p i n c h o f f v o l t a g e at which no I  the I  defined  on  The  the 0.9cmxl.5cm sample, 3 a r r a y s of MESFET w i t h approximately  per a r r a y were f a b r i c a t e d .  f u n c t i o n a l , the remaining alignment  106  Out  of these 366  MESFET, 260  n o n - f u n c t i o n a l MESFET having  so that the channel c o u l d not be  pinched  off.  120  MESFET were  bad  gate  F i g . 4.4  shows p a r t  F i g . 4.4 MESFET a r r a y ( M a g n i f i e d 300X)  on sample 2 8 3 - S 1 1  56  of a f a b r i c a t e d MESFET a r r a y .  A typical I  MESFET are shown i n F i g . 4.5.  H y s t e r e s i s loops i n the ^ g - V p g  F i g . 4.5  are o f t e n observed i n GaAs MESFET  t r a p p i n g and  F i g . 4.7  sample.  characteristics for  Uo  [33,68],  A t y p i c a l I - -V curve DS GS  these  curves  of  They are a t t r i b u t e d to  r e - e m i t t i n g of c a r r i e r s from deep l e v e l traps present  channel r e g i o n . 4.6.  -V  Uo  i n the  of these MESFET i s shown i n F i g .  shows the v a r i a t i o n of V , f o r the 3 MESFET a r r a y s a c r o s s th  the  I t can be seen that the s c a t t e r i n g of V , i s more n o t i c e a b l e f o r th  MESFET l o c a t e d on the l e f t a r r a y of MESFET (3rd a r r a y ) the m e t a l l i z a t i o n and  h a l f of the after  sample.  the d i s l o c a t i o n e t c h .  the SigN^ f i l m , but  hence the l o c a t i o n of the gates  are s t i l l  To check the r e l a t i o n s h i p of V d i s l o c a t i o n , a s c a t t e r p l o t of V f o r a l l the f u n c t i o n a l MESFET was  The  clearly  w i t h d i s t a n c e to the  F i g . 4.9  According  the  e t c h removed and  nearest  a g a i n s t the g a t e - t o - n e a r e s t - p i t made.  of  visible.  distance  i n d i c a t e s t h a t t h e r e i s no  from a n e a r e s t  t h a t found by Winston et a l . [67]  t h a t by Miyasawa e t a l . [64].  shows one  the l o c a t i o n of ohmic pads  d i r e c t dependence of MESFET V , on i t s d i s t a n c e th T h i s r e s u l t agrees w i t h  F i g u r e 4.8  and  dislocation.  disagrees  to Winston e t a l . , one  of  with  the  p o s s i b l e reasons f o r Miyasawa et a l . to observe a c o r r e l a t i o n between V t h and  d i s t a n c e to n e a r e s t d i s l o c a t i o n i s that t h e i r  from randomly s e l e c t e d MESFET along f i n d i n g was  ^.  r e l a t i o n s h i p between a MESFET's V ^ and d i s l o c a t i o n , Winston et a l . [67]  c o n s i s t e d of  the diameter of a whole wafer so  the r e s u l t of superimposing d i s t r i b u t i o n s  d i f f e r e n t d i s l o c a t i o n d e n s i t y and V  investigated  study  1° 8  e t  a true  i t s distance  from r e g i o n s  may  their  of  microscopic to a  nearest  suggested a s m a l l l i m i t e d  i n s t e a d of a l a r g e area where the EPD  data  vary  area  should  be  considerably.  57  Fig.  4.5  from  the device  V__  bias  I c- r Q v  r i  : -0.2  1  characteristics  array V/  on  step  sample  o f MESFET 283-S11.  58  Fig.  4 . 6 Typical  sample  283-S11  I  D  S  -  V G  S  characteristics  for  ++  + +  + \ v v  + ++  +  30  48 Dlst. across  25  45 Dlst. across  66 the  65 the  84 array  1st  * + +  102 ( . 1 1 E - 3 m)  85 array  2nd  ++  105 C.11E-3  m)  120  125  ~2.75 > I  w  2.2  a o  > o  1.65  :* *  +  +  +  %*  + +  A *"  +*>  1.1 .55  25  Fig.  4.7  45 Dlst.  65 across 3rd  Variation  MESFET a r r a y s  85 array  of V  on sample  T H  105 ( . 1 1 E - 3 m)  across  283-S11  125  the three  Fig. 4.8 MESFET a r r a y a f t e r d i s l o c a t i o n e t c h network s t r u c t u r e (b) Right h a l f o f the a r r a y  (a) L e f t h a l f of the a r r a y showing showing l e s s e r organized l i n e structure  O  2.75  2.3  1.85  1.4  ,95  -  0  20 Dist.  Fig*  4.9  sample  Plot  283-S11  of V  T H  40 to nearest  60 p i t (microns)  vs d i s t a n c e t o n e a r e s t  60  p i t f o r MESFET  100  from  62  As F i g . 4.8  shows, the d i s l o c a t i o n networks change from  the  honeycomb-like s t r u c t u r e s on the l e f t - h a n d h a l f of the 3 r d MESFET a r r a y ( F i g . 4.8a)  to wavy l i n e s on the r i g h t - h a l f ( F i g . 4.8b).  the d i s t r i b u t i o n of V F i g . 4.10a  Two  histograms  along the 3 r d MESFET a r r a y i s shown i n F i g .  of  4.10.  i s f o r those MESFET on areas w i t h honeycomb network s t r u c t u r e s  and F i g . 4.10b  i s f o r those on areas with wavy l i n e s .  that s c a t t e r i n g  F i g u r e 4.10  of MESFET V ^ c o u l d be dependent upon the  indicates  dislocation  network i n which the s c a t t e r i n g i s more n o t i c e a b l e i n areas w i t h honeycomb d i s l o c a t i o n network s t r u c t u r e s .  T h i s r e s u l t has a l s o been observed  by I s h i i  shows two  et a l . [ 6 5 ] .  F i g . 4.11  of leakage c u r r e n t along the 3 rd S c h o t t k y  histograms pad  array.  of the The  before  distribution  scattering i s  again more severe f o r pads on areas w i t h honeycomb networks than those areas without  the honeycomb networks.  above, the d i s l o c a t i o n network may characteristics the l o c a l EPD  T h e r e f o r e , from the o b s e r v a t i o n  be one  of the major causes  s c a t t e r i n g i n undoped LEC-GaAs.  i s shown i n F i g . 4.12.  on  L o c a l EPD  for device  A p l o t of MESFET V i n t h i s experiment  ^ versus was  the  amount of e t c h p i t s l o c a t e d i n an area of 200umx200um centered on each MESFET. EPD. be  F i g . 4.13  shows a p l o t of MESFET I  From F i g s . 4.12  and 4.13  at zero gate b i a s v e r s u s  no dependent of V  f c h  and I  on l o c a l EPD  local can  observed. To  summarize, no d i r e c t c o r r e l a t i o n between d e v i c e c h a r a c t e r i s t i c s  and d i s l o c a t i o n s was  found.  The  s c a t t e r of d e v i c e c h a r a c t e r i s t i c s was  severe i n areas of o r g a n i z e d c e l l u l a r network s t r u c t u r e s i m p l y i n g that h i g h l y uniform and low d i s l o c a t i o n s ( t o a v o i d the f o r m a t i o n of  cellular  network s t r u c t u r e s ) GaAs c r y s t a l s are r e q u i r e d f o r f u t u r e d i r e c t  more  63  10  E  UJ  C  0 -1.0  -2.0  -15  -25  ( V)  TH  (a)  10 H  QJ  -£  E  5 •  r-  uJ  Lu  °-1.0  -1.5  -Z5  -2D IV)  TH  (b) Fig.  4.10  for  FET  (b)  Right  Histograms  along half  of  the  the  (a)  Left  of  3rd  array  d i s t r i b u t i o n of  half  of  3rd array  V  T H  (Fig. 4.8)  QJ -£ £ D  r-  LU U-  C  0  4 5 6 7 8 9 10 LEAKAGE CURRENT ( pA ) ( a)  2$ E  r -  ^ 0  4  5  LEAKAGE  —i—i—i  r  6 7 CURRENT(pAl  (b)  F i g . 4.11 Histograms of the d i s t r i b u t i o n of leakage c u r r e n t f o r FET a l o n g t h e ( a ) L e f t h a l f o f 3rd a r r a y (b) R i g h t h a l f o f 3rd a r r a y  2.75  10  20  Local  Fig.  4.12  from  sample  Plot  of  283-S11  V  T H  30  dislocation  vs  local  density  dislocation  40 (.25E4/cm^2)  density  for. MESFET  50  450  n  0  Fig.  4.13  10 Local  20 dislocation  Plot of I  D  S  30 40 d e n s i t y (.25E4/cm~2)  ( g V =0 V ) vs l o c a l Q S  d e n s i t y f o r MESFET f r o m s a m p l e 283-S11  dislocation  67  i m p l a n t a t i o n l a r g e s c a l e i n t e g r a t i o n technology. V ^ i 51].  n  t h i s experiment  V a r i a t i o n o f the MESFET  i s l a r g e r than those r e p o r t e d by o t h e r a u t h o r s [63-  The s c a t t e r of d e v i c e c h a r a c t e r i s t i c s i n t h i s experiment  p a r t l y due to f a b r i c a t i o n process induced inhomogenity. s e r v e s as i n i t i a l  experiment  run f o r the study of the e f f e c t s o f d i s l o c a t i o n s on d e v i c e  f a b r i c a t e d on undoped SI LEC GaAs u s i n g d i r e c t U.B.C.  This  was p r o b a b l y  i m p l a n t a t i o n technology a t  I n f u t u r e s t u d i e s , the c o n t r i b u t i o n to the s c a t t e r from s u b s t r a t e  and p r o c e s s induced inhomogenity  should be separated and a n a l y z e d , and the  r e s u l t s o b t a i n e d i n t h i s experiment purposes.  can then be used  f o r comparison  68  CHAPTER 5 BACKGATING IN GaAs MESFET  5.1  Introduction The  v a r i a t i o n of MESFET d r a i n c u r r e n t c h a r a c t e r i s t i c s due  to a nega-  t i v e b i a s a p p l i e d to a c o n t a c t on  the back of a s u b s t r a t e or nearby on  front  [69-73].  ing  f a c e i s known as backgating  In integrated c i r c u i t s ,  c o u l d cause unwanted communication between d e v i c e s with  r e s u l t s even though SI s u b s t r a t e s were used. backgating  a l l y stable slices p l a c e d u r i n g high placed  should  be used so that no  temperature anneal,  and  i n f l u e n c e of  (1) high r e s i s t i v i t y , surface conversion  (2) c r i t i c a l  f a r enough away from a n e g a t i v e v o l t a g e  l e s s s e n s i t i v e to b a c k g a t i n g ,  take  components should  source  be  so that the FET  (3) d e v i c e i s o l a t i o n can be  However, b a c k g a t i n g  therm-  can  is  increased  p r o t o n bombardment i n s e l e c t i v e areas of SI s u b s t r a t e as proposed D'Avanzo [ 7 9 ] .  backgat-  unpredictable  This undesirable  can be minimized by v a r i o u s means:  the  by  by  remains a problem i n the development of  GaAs IC. In the f i r s t  p u b l i s h e d work, the backgate b i a s (V  ) was  a p p l i e d to  BG e l e c t r o d e s on the back of s u b s t r a t e and  changes i n I  were observed f o r  samples f a b r i c a t e d on an e p i t a x i a l l a y e r on Cr-doped SI GaAs [74,75]. space charge r e g i o n i s present and  i t s m o d u l a t i o n was  charge r e g i o n was in  e l e c t r o d e , the  at the e p i t a x i a l l a y e r - S I s u b s t r a t e i n t e r f a c e  b e l i e v e d to be  involved i n backgating.  shown to be a f f e c t e d by the nature  the i n t e r f a c e [ 7 5 ] .  A  When a n e g a t i v e  of the  This  trapping  b i a s i s a p p l i e d to the  space levels  backgating  space charge r e g i o n expands by an amount which depends on  the  c o n c e n t r a t i o n s of the t r a p p i n g l e v e l s .  The  expansion of the i n t e r f a c e  space  charge r e g i o n d e c r e a s e s the a c t i v e channel and thus cause a decrease i n  R e c e n t l y , b a c k g a t i n g has been s t u d i e d i n i o n implanted MESFET on SI s u b s t r a t e w i t h the b a c k g a t i n g c o n t a c t on the same s i d e of the wafer as the FET.  Kocat and S t o l t e  [70]  r e p o r t e d that the e l e c t r o n l e v e l EL2  i n b a c k g a t i n g f o r undoped SI LEC GaAs w h i l e both EL2 t r a p mentioned i n Ch. 2 are i n v o l v e d al.  [76]  and the C r - r e l a t e d  f o r Cr-doped SI GaAs.  Backgating was  than h i g h duty c y c l e . backgate-source  found  to be more severe f o r low duty  I n f a c t , f o r a duty c y c l e of 1 0  b i a s of -2.5V, the d r a i n c u r r e n t was  w h i l e no change was  observed at u n i t duty c y c l e .  - 3  and an  reduced  Lee e t a l .  cycle  percent  [72] and  Miers  and  They propose that f o r h i g h r e s i s t i v i t y m a t e r i a l s , a t  low b a c k g a t i n g v o l t a g e s , the s u b s t r a t e c o n d u c t i o n i s c o n t r o l l e d t h e r m a l l y generated c a r r i e r s so t h a t an ohmic I-V  by the  r e l a t i o n i s expected.  When the a p p l i e d v o l t a g e reaches a c r i t i c a l v a l u e , the c u r r e n t was rise  b i a s e d by  average  by 40  [73] have d i s c u s s e d the r e l a t i o n s h i p between b a c k g a t i n g  substrate conduction.  hole  B i r r i t t e l l a et  i n v e s t i g a t e d b a c k g a t i n g w i t h the source v o l t a g e of a FET  a pulse t r a i n .  et a l .  i s involved  s h a r p l y and t h i s was  believed  to be the occurrence of a  found to  trap-filled-  l i m i t at a voltage V  . V i s reached when the i n j e c t e d c a r r i e r s from the TFL TFL up the deep t r a p s i n the s u b s t r a t e [ 7 7 ] . Lee et a l . [72]  backgate  filled  observed  that the V  Tr L  of s u b s t r a t e c o n d u c t i o n c o i n c i d e d w i t h the onset  v o l t a g e of the b a c k g a t i n g e f f e c t (V of 2.5V,  BTH  ).  good agreement between V,,-,, and V Din  but not i n Cr-doped HB GaAs.  For M i e r s e t a l . [ 7 3 ] , w i t h a V uo  lrL  However, a t a V  was  observed  i n SI LEC GaAs  o f lOOmV, good  correlation  70  was  observed  above, a V  i n both LEC and V  BTH  TFL  and HB m a t e r i a l s .  of 5V  BTH  concluded  and V  TFL  that c a r r i e r  the b a c k g a t i n g e f f e c t .  papers  i s g e n e r a l l y obtained f o r a s e p a r a t i o n of 30pm  to 40pm between the s i d e g a t e and MESFET. between V  A c c o r d i n g to the two  observed  Due  to the good  correlation  by Lee et a l . and M i e r s e t a l . ,  i n j e c t i o n into  they  the s u b s t r a t e i s d i r e c t l y r e l a t e d  to  A more r e c e n t paper ( a l s o by the same group as Lee  e t a l . [72]) by Chang et a l . phenomenon i n more d e t a i l .  [78]  studied  the s u b s t r a t e c o n d u c t i o n  They b e l i e v e that the V  observed by Lee e t TFL  al.  [72] and M i e r s e t a l . [73] was  of f i l l i n g  much too low to s a t i s f y the  requirement  up a l l the deep l e v e l s i n the SI GaAs between the backgate  the MESFET.  I n s t e a d , Chang e t a l .  o u t d i f f u s e s d u r i n g h i g h temperature  proposed  that the deep l e v e l  anneal and  C u r r e n t c o n d u c t i o n between the backgate  EL2  l e a v i n g behind a t h i n  uncompensated l a y e r (p-type) on the s u r f a c e between the backgate FET.  and  and  the FET  and  the  then takes p l a c e  on the s u r f a c e d e p l e t i o n r e g i o n o f t h i s p l a y e r .  5.2  Experimental Procedures To  and R e s u l t s  i n v e s t i g a t e d e v i c e i s o l a t i o n and  substrate (or surface) conduction  i n MESFET f a b r i c a t e d on SI<100>LEC GaAs at U.B.C, b a c k g a t i n g were performed  u s i n g a c o n t a c t nearby  i n t h i s experiment  were f a b r i c a t e d by T a r r [81] and Lau  measured f o r other purposes 5.1,  on the f r o n t f a c e .  by Lowe [ 3 3 ] .  they are p a r t o f a t e s t a r r a y that was  Two  the  shown on the l e f t  d e v i c e s used  [82] and were  t r a n s i s t o r s are shown i n F i g .  f a b r i c a t e d on s l i c e 45-S92.  MESFET w i t h the 500pm wide and 20pm long gate was l a r g e ohmic pad  The  experiments  used  i n t h i s study.  hand s i d e (700pm s e p a r a t i o n ) was  used  The The as  Fig.  5.2  MESFET o f s a m p l e  123-S131  72  backgating ple  electrode.  o f the second  I n F i g . 5.2, the t r a n s i s t o r i n the middle  i s an exam-  s t r u c t u r e t h a t was a l s o examined i n t h i s experiment.  type o f FET has a 20pm wide and 3 pm long gate and was f a b r i c a t e d  on  123-S131.  An ohmic pad p l a c e d 250 pra from the MESFET was used as a  backgating  electrode.  at  850°C, u s i n g S i 0  of  these d e v i c e s i s g i v e n i n Ref. 33.  cap i n both c a s e s .  The complete f a b r i c a t i o n  A b l o c k diagram of the e x p e r i m e n t a l Fig. V.  The a c t i v e l a y e r of 45-S92 was  by a n n e a l i n g a t 800°C f o r 20 minutes w h i l e 123-S131 was 2  5.4 shows a t y p i c a l I  n  -V  annealed procedure  s e t up i s shown i n F i g . 5.3.  c h a r a c t e r i s t i c s o f sample 123-S131 w i t h  F i g . 5.5 shows the I -V DS DS c h a r a c t e r i s t i c s 'of the same sample w i t h V a t 0V and V „ stepped from 0 t o GS BG c  stepped  slice  Both s t r u c t u r e s , samples 45-S92 and 123-S131, were  f a b r i c a t e d using d i r e c t i o n implantation. activated  This  from 0 to -8V and V__  h e l d at 0V.  np  JSG  -12V.  The r e s u l t  from F i g . 5.5 shows t h a t the backgating  s t r o n g and can even p i n c h o f f the a c t i v e channel  i n f l u e n c e was  i f a l a r g e enough  b a c k g a t i n g b i a s i s present nearby.  A p l o t of I_. -V with V stepped from DS GS BG 0 t o -8V i s shown i n F i g . 5.6 and i t shows a c l e a r dependence of V ^ on V . The  r e s u l t s from F i g s . 5.5 and 5.6 c o n f i r m the e f f e c t of V  c h a r a c t e r i s t i c s as r e p o r t e d i n many papers  [69-76].  BG  on d e v i c e  F i g . 5.7  1 -V c h a r a c t e r i s t i c s f o r sample 45-S92 w i t h V _ stepped DS Go BG n  shows the  from 0 t o -30V.  Comparison o f F i g s . 5.6 and 5.7 shows t h a t the magnitude o f b a c k g a t i n g e f f e c t s i s dependent on the s e p a r a t i o n between the d e v i c e and s i d e g a t e . V__„ o f a p p r o x i m a t e l y -5V was found BTH [73]  and B i r r i t t e l l a  et a l .  « 0V ( F i g s . 5.8 and 5.9).  i n r e p o r t s by Lee e t a l . [ 7 2 ] , M i e r s  [ 7 6 ] . The MESFET i n t h i s experiment  That i s , the onset o f backgating  have V-,-,.. Bin  occurred with  SAMPLE BACKGATE  1 •  » »  11—[ r-  -==.  1  4-t=i  11  1  SEMICONDUCTOR  WENTWORTH MULTI-PROBES STATION Fig.  5.3  HP A145A  Block-diagram  PARAMETER  HP  7475A  PLOTTER  ANALYZER  of backgating  experimental  s e t up  V  B G  =  0  V  .JN  V  D S  = 1.25V  00  VO  80  these p a r t i c u l a r samples as soon as t h e r e e x i s t e d a n e g a t i v e l y c o n t a c t nearby. that S i 0 used by  2  the I rose  BG  major d i f f e r e n c e between the  (I__) was BG  experiment was  BG  observed.  generally greater The  by Lee  c o r r e l a t i o n between V  The  v a l u e of V , TFL riTr  than -30  et a l . [72]  and V  V where V  .  and  orders  temperature anneal and  s u r f a c e and  The  BTH  (V  TFL  obtained of the and V  TFL  show  The )  I  il+  in this  same samples implies  that  origin  observed a c l o s e  /cm  under the  3  I t has  may  been shown by  concentration  surface after a  t h a t caused t h i s s u r f a c e l a y e r to be  o u t d i f f u s i o n of EL2 a n -p-n  the ohmic c o n t a c t  +  thus induced +  channel i n t e r f a c e would be r e v e r s e  +  decreased  by  high  under-  a t h i n p - l a y e r under  the  j u n c t i o n between the backgate  of the MESFET.  a p p l i e d to the backgate, the p-n  As  soon as a n e g a t i v e  j u n c t i o n at the  biased  bias  substrate-active  so the d e p l e t i o n r e g i o n would  i n t u r n reduced the a c t i v e l a y e r .  by the FET  who  BG  was  A s u r f a c e c o n v e r s i o n model [78]  that the deep l e v e l EL2  therefore created  e l e c t r o d e and  widen and  and 5.11  BTH  of magnitude to 1 0  compensated.  T  BTH  M i e r s [73]  the o b s e r v a t i o n made i n t h i s experiment.  Makram-Ebeid et a l . [80]  felt  F i g s . 5.10  disagreement between V  TFL  is  .  e f f e c t s observed i n t h i s experiment were of d i f f e r e n t  than those r e p o r t e d  was  BG  but when a c e r t a i n t h r e s h o l d v o l t a g e  were a p p r o x i m a t e l y OV. the backgating  was  backgating  p l o t s f o r samples 45-S92 and 123-S131, r e s p e c t i v e l y .  reached a sudden r i s e was  two  i n the SI s u b s t r a t e , the  measured as a f u n c t i o n of V  s l o w l y at low V  explain  Sigt^  was  authors.  i n v e s t i g a t e current conduction  -V__ BG  f a b r i c a t i o n procedure  used as the encapsulant i n t h i s experiment w h i l e  the above To  current  was  One  biased  For  t h i s model, the  immediately a f t e r the a p p l i c a t i o n of a n e g a t i v e  backgating bias  and  00  to  83  V  BTH  i s t h e r e f o r e OV.  current  The  I  through the n - p - n +  +  BG  a t low  backgating  junction.  to the breakdown of the r e v e r s e b i a s e d the  s u r f a c e d e p l e t i o n r e g i o n of the  all  the deep l e v e l s . To  (1) are (2)  The p-n  b i a s could be  sudden r i s e  +  BTH  BG  leakage  could  be  j u n c t i o n or the c o n d u c t i o n  p-layer a f t e r injected c a r r i e r s  due in  filled  summarize:  I„„ decreased as V„„ i n c r e a s e d and c o r r e s p o n d i n g l y DS BG s e n s i t i v e to a n e g a t i v e l y b i a s e d c o n t a c t nearby. V  in I  the  was  found to be OV  t h i s experiment.  while V  TFL  was  greater  A good c o r r e l a t i o n between V  than -30V  and V  TFL  was  f o r devices observed  Lee  et a l . [72]  and  the  use  as e n c a p s u l a n t f o r samples 45-S92 and 123-S131 i n s t e a d  of S i 0  2  M i e r s et a l . [73].  BTH  the V , of MESFET th  T h i s d i f f e r e n c e i s probably  due  by to of  SI3V (3)  A  surface conversion  experiment was activation  explained  anneal.  model was  presented  i n which backgating  by a p - l a y e r formed a f t e r a high  in this  temperature  in  84  CHAPTER 6 CONCLUSIONS AND  SUGGESTIONS FOR  FUTURE WORK  I n c o n c l u s i o n , the f o l l o w i n g o b s e r v a t i o n s can be made: (1)  The  DLTS e x p e r i m e n t a l  set up was  work.  U s i n g t h i s experiment,  slices  from  improved d u r i n g the course of  t h r e e e l e c t r o n t r a p s were d e t e c t e d i n a l l f o u r  four d i f f e r e n t SI GaAs i n g o t s .  are c h a r a c t e r i s t i c s of GaAs from Cominco. l e v e l s were found  to be 0.80,  0.72  a s s o c i a t e d w i t h , as c l a s s i f i e d respectively.  T h i s suggests The  and 0.52  of 0.65  These l e v e l s were  by M a r t i n et a l [17], EL2, E L I 2 ,  eV was  to a t r a p w i t h an  and Fairman e t a l .  [32].  Thermally  f o r compensating  i o n i m p l a n t a t i o n induced (2)  A  by O l i v e r et a l . to  shallow a c c e p t o r s i n  (0.80eV) to P2  For f u t u r e work, the  measurement should be extended  electron  s t a b l e s l i c e s obtained from Cominco were  shown to have h i g h e r peak h e i g h t r a t i o of PI thermally unstable s l i c e s .  observed  EL4,  T h i s l e v e l i s b e l i e v e d by these authors  be r e s p o n s i b l e , t o g e t h e r w i t h EL2, undoped SI LEC GaAs.  and  d e t e c t e d i n the t h i n sample 86-T.  n e g a t i v e peak w i t h s i m i l a r a c t i v a t i o n energy was [30]  t h a t these t r a p s  a c t i v a t i o n e n e r g i e s of these  eV.  A n e g a t i v e peak c o r r e s p o n d i n g  a c t i v a t i o n energy  this  eV)  than  photocurrent-DLTS  to study process induced  t r a p s and  (0.72  traps.  For  example,  s t r e s s induced t r a p s .  I n the i n v e s t i g a t i o n of d i s l o c a t i o n s and  s c a t t e r of the t h r e s h o l d v o l t a g e V ^ was  found  device c h a r a c t e r i s t i c s ,  the  to be h i g h e r on areas of  c e l l u l a r d i s l o c a t i o n networks than on areas w i t h j u s t wavy l i n e s o f dislocations. induced  V a r i a t i o n of d e v i c e c h a r a c t e r i s t i c s was  inhomogenity  p a r t l y due  to process  and no c o r r e l a t i o n between d e v i c e c h a r a c t e r i s t i c s  and  85  d i s l o c a t i o n s was  established.  I n f u t u r e study of the e f f e c t  of  d i s l o c a t i o n s , a whole wafer should be used so t h a t the macroscopic can be examined along with the m i c r o s c o p i c v a r i a t i o n . a l s o be designed contributed (3)  to e l i m i n a t e as f a r as p o s s i b l e the  from the f a b r i c a t i o n  In the b a c k g a t i n g  MESFET were examined. backgating  was  backgating.  should  inhomogenity  process.  experiment, the e f f e c t of nearby c o n t a c t s on I For the p a r t i c u l a r  under a S i 0  2  cap.  of  samples t h a t were s t u d i e d ,  formed a f t e r a high temperature a n n e a l .  examined were annealed and  experiment  e x p l a i n e d by a s u r f a c e c o n v e r s i o n model i n which a  s u r f a c e l a y e r was  encapsulant  The  variation  The  p-type  samples  In f u t u r e work, d i f f e r e n t  a n n e a l i n g c o n d i t i o n s should be used to t e s t  types of  the n a t u r e  of  86  REFERENCES 1.  A.M. Huber, G. M o r i l l o t , N.T. L i n h , P.N. Favennec, B. Deveaud and T o u l o u s e , "Cr p r o f i l e s i n SI GaAs a f t e r a n n e a l i n g w i t h a SigN^ encapsulant", A p p l . Phys. L e t t . 34(12), 858 (1979).  B.  2.  B. Tuck, G.A. Adegloyega, P.R. Joy and M.J. C a r d w e l l , " O u t - d i f f u s i o n o f chromium from GaAs s u b s t r a t e s " , GaAs and r e l a t e d compounds, I n s t . Phys. Conf. Ser. 45, 114 (1978) .  3.  G.R. C r o n i n and R.W. H a i s t y , "The p r e p a r a t i o n of s e m i - i n s u l a t i n g g a l l i u m a r s e n i d e by chromium doping", J . E l e c t r o c h e m . S o c , 111(7), (1964).  875  4.  C.H. Gooch, C. Hilsum, and B.C. Holeman, " P r o p e r t i e s of s e m i - i n s u l a t i n g GaAs", J . A p p l . Phys., s u p p l . 32(10), 2069 (1961 ) .  5.  E.P.A. Metz, R.C. M i l l e r , and R. Mazelsky, "A technique f o r p u l l i n g s i n g l e c r y s t a l s of v o l a t i l e m a t e r i a l s " , J . A p p l . Phys., 3 3 ( 6 ) , 2016 (1962).  6.  J.B. M u l l i n , R.J. H e r i t a g e , C.H. H o l l i d a y , and B.W. Straughan, " L i q u i d e n c a p s u l a t i o n c r y s t a l p u l l i n g at h i g h p r e s s u r e s " , J . C r y s t a l Growth 3 ( 4 ) , 281 (1968).  7.  G.M. M a r t i n , J.P. Farges, G. Jacob, J.P. H a l l a i s , and G. P o r b l a n d , "Compensation mechanisms i n GaAs", J . A p p l . Phys., 5 1 ( 5 ) , 2840 (1980).  8.  D.E. Holmes, R.T. Chen, K.R. E l l i o t t , and C.G. K i r k p a t r i c k , " S t o i c h i o m e t r y - c o n t r o l l e d compensation i n l i q u i d encapsulated C z o c h r a l s k i GaAs", A p p l . Phys. L e t t . , 4 0 ( 1 ) , 46 (1982).  9.  E . J . Johnson, J.A. K a f a l a s , and R.W. D a v i e s , "The r o l e of d e e p - l e v e l c e n t e r s and compensation i n producing s e m i - i n s u l a t i n g GaAs", J . A p p l . Phys., 54(1), 204 (1983) .  10.  A. M i r c e a , A. Mitonneau, L. H o l l a n , and A. B r i e r e , " O u t d i f f u s i o n of deep e l e c t r o n t r a p s i n e p i t a x i a l GaAs", A p p l . Phys. 11, 153 (1976).  11.  A.M. Huber, N.T. L i n h , M. V a l l a d o n , J . L . Debrun, G.M. M a r t i n , A. Mitonneau, and A. M i r c e a , " D i r e c t evidence f o r the nonassignment to oxygen of the main e l e c t r o n t r a p i n GaAs", J . A p p l . Phys., 50(6), 4022 (1979).  12.  J . Lagowski, H.C. Gatos, J.M. Parsey, K. Wada, M. Kaminska, and W. Walnkiewicz, " O r i g i n of the 0.82-ev e l e c t r o n t r a p i n GaAs and i t s a n n i h i l a t i o n by shallow donors", A p p l . Phys. L e t t . , 4 0 ( 4 ) , 342 (1982).  13.  E.R.  Weber, H. Ennen, U. Kaufmann, J . Windschief  and J .  Schneider,  87  " I d e n t i f i c a t i o n of A s a n t i s i t e s i n p l a s t i c a l l y deformed GaAs", J . A p p l . Phys., 53 ( 9 ) , 6140 (1982). G  14.  K. E l l i o t t , R.T. Chen, S.G. Greenbaum, R.J. Wagner, " I d e n t i f i c a t i o n of A S g a n t i s i t e d e f e c t s i n l i q u i d encapuslated C z o c h r a l s k i GaAs", A p p l . Phys. L e t t . , 44 ( 9 ) , 907 (1984). a  15.  G.M. M a r t i n and S. Makram-Ebeid, " M a n i f e s t a t i o n s d e f e c t s i n GaAs", P h y s i c a 116B, 371 (1983).  16.  D.V. Lang, "Deep l e v e l t r a n s i e n t spectroscopy: A new method to c h a r a c t e r i z e traps i n semiconductors", J . of A p p l . Phys. 4 5 ( 7 ) , 3023 (1974).  17.  G.M. M a r t i n , A. Mitonneau, A. M i r c e a , " E l e c t r o n t r a p s i n b u l k e p i t a x i a l GaAs c r y s t a l s " , E l e c t r o n L e t t . 13(7 ), 191 (1977 ) .  and  18.  A. Mitonneau, G.M. M a r t i n , A. M i r c e a , "Hole t r a p s i n bulk and GaAs c r y s t a l s " , E l e c t r o n . L e t t . 13(22), 666 (1977).  epitaxial  19.  F. Hasegawa, N. Iwata, N. Yamamoto, and Y. N a n n i c h i , " D i s t r i b u t i o n of the main e l e c t r o n t r a p EL2 i n undoped LEC GaAs", Jap. J . of A p p l . Phys. 2 2 ( 8 ) , L502 (1983) .  20.  M.G. A d l e r s t e i n " E l e c t r i c a l L e t t . 12(12), 297 (1976).  21.  C. Hurtes, M. Boulou, A. Mitonneau and D. B o i s , "Deep l e v e l s p e c t r o s c o p y i n h i g h r e s i s t i v i t y m a t e r i a l s " , A p p l . Phys. L e t t . 32(12), 821 (1978).  22.  R.D. Fairman, F . J . Morin and J.R. O l i v e r , "The i n f l u e n c e of semii n s u l a t i n g s u b s t r a t e s on the e l e c t r i c a l p r o p e r t i e s of h i g h p u r i t y GaAs b u f f e r l a y e r s grown by vapor-phase e p i t a x y " , GaAs and r e l a t e d Compounds, I n s t . Phys. Conf. s e r . 45, 134 (1978).  23.  G.M. M a r t i n and D. B o i s , "A new levels i n insulating materials: i n s u l a t i n g GaAs", Semiconductor Barnes e d i t o r , E l e c t r o c h e m . Soc.  24.  R.D. Fairman and J.R. O l i v e r , "Grwoth and c h a r a c t e r i z a t o n of semii n s u l a t i n g GaAs f o r use i n i o n i m p l a n t a t i o n " , S e m i - i n s u l a t i n g III-V M a t e r i a l s , G. Rees e d i t o r , Shiva p u b l i s h i n g , 83 (1980).  25.  B. Deveaud and B. T o u l o u s e , " O b s e r v a t i o n of very deep l e v e l s by DLTS", S e m i - i n s u l a t i n g III-V M a t e r i a l s , G. Rees e d i t o r , S h i v a p u b l i s h i n g , 241 (1980) .  26.  T.  I t o h and  H. Y a n a i ,  of deep l e v e l s  point  t r a p s i n GaAs microwave FETS", E l e c t r o n .  technique f o r the s p e c t r o s c o p y of deep A p p l i c a t i o n to the study of semiC h a r a c t e r i z a t i o n Techniques, P.A. P r o c . 78-3, 32 (1978).  optical  "Experimental i n v e s t i g a t i o n of i n t e r f a c e traps  88  i n GaAs p l a n a r d e v i c e s by DLTS and PITS methods", GaAs and compounds, I n s t . Phys. Conf. s e r . 56, 537 (1980).  related  27.  J.K. Rhee, P.K. B h a t t a c h a r y a and R.Y. Koyama, "Deep l e v e l s i n S i implanted and t h e r m a l l y annealed s e m i - i n s u l a t i n g GaAsrCr", J . A p p l . Phys. 53(4), 3311 (1982).  28.  Y. Yuba, K. Gamo and S. Namba, "Deep l e v e l s i n implanted and l a s e r annealed GaAs s t u d i e d by c u r r e n t - and c a p a c i t a n c e - t r a n s i e n t measurements", GaAs and r e l a t e d Compounds, I n s t . Phys. Conf. s e r . 63, 221 (1981 ) .  29.  M. Ogawa, T. Kamiya, and H. Y a n a i , "Appearance o f a n e g a t i v e peak i n the PITS spectrum from GaAs LEC s i m i - i n s u l a t i n g c r y s t a l s " , GaAs and r e l a t e d Compounds, I n s t . Phys. Conf. s e r . 63, 571 (1981).  30.  J.R. O l i v e r , R.D. Fairman and R.T. Chen, "Undoped s e m i - i n s u l a t i n g LEC GaAs. A model and a mechanism", E l e c t r o n L e t t , 839 (1981).  31.  C. Hurtes, L. H o l l a n and M. Boulou, "Impurity c h a r a c t e r i z a t i o n of GaAs h i g h - r e s i s t i v i t y VPE l a y e r s f o r FET d e v i c e s " , GaAs and r e l a t e d compounds, I n s t . Phys. Conf. s e r . 45, 342 (1978).  32.  R.D. Fairman, R.T. Chen, J.R. O l i v e r and D.R. Chen, "Growth of h i g h p u r i t y s e m i - i n s u l a t i n g bulk GaAs f o r i n t e g r a t e d - c i r c u i t a p p l i c a t i o n s " , IEEE T r a n s . E l e c t r o n D e v i c e s , 2 8 ( 2 ) , 135 (1981). K.S. Lowe, "Ion-implanted GaAs MESFET t e c h n o l o g y " , M.A.Sc. T h e s i s , U.B.C, 50 (1983) .  33.  34.  C T . Sah, L. Forbes, L.L. R o s i e r and A.F. Tasch, J r . , "Thermal and o p t i c a l e m i s s i o n and capture r a t e s and c r o s s s e c t i o n s i n semiconductors from photo and dark j u n c t i o n c u r r e n t and c a p a c i t a n c e experiments", S o l i d S t a t e E l e c t . 13, 759 (1970).  35.  D.H. Rumsby and R.M. Ware, "The e f f e c t o f the water content o f the b o r i c oxide encapsulant on the p u r i t y and s t o i c h i o m e t r y of LEC GaAs", GaAs and R e l a t e d Compounds, I n s t . Phys. Conf. s e r . 63, 573 (1981).  36.  L.B. Ta, R.N. Thomas, G.W. E l d r i d g e , and H.M. Hobgood, " R e p r o d u c i b i l i t y and u n i f o r m i t y c o n s i d e r a t i o n s i n LEC grown of undoped, s e m i - i n s u l a t i n g GaAs f o r l a r g e - a r e a d i r e c t i m p l a n t a t i o n technology", GaAs and r e l a t e d Compounds, I n s t . Phys. Conf. s e r . 65, 31 (1982).  37.  P. P e t r o f f and R.L. Hartman, "Defect s t r u c t u r e i n t r o d u c e d d u r i n g o p e r a t i o n o f h e t e r o j u n c t o i n GaAs l a s e r s " , A p p l . Phys. L e t t . , 2 3 ( 8 ) , (1973) .  38.  A.S. J o r d a n , R. Caruso, and A.R. Von Neida, "A t h e r m o e l a s t i c a n a l y s i s o f d i s l o c a t i o n g e n e r a t i o n i n p u l l e d GaAs c r y s t a l s " , The system Tech. J o u r n a l , 59 (4 ), 503 (1980).  469  Bell  89  39.  J . A n g i l e l l o , R.M. Potemski, and G.R. Woolhouse, " E t c h p i t s and d i s l o c a t i o n s i n {100} GaAs wafers", J . A p p l . Phys., 4 6 ( 5 ) , 2315 (1975 ) .  40.  M.S. Abrahamas and C.J. B u r o c c h i , " D i s l o c a t i o n s and p r e c i p i t a t e s i n GaAs i n j e c t i o n L a s e r s " , J . A p p l . Phys., 3 7 ( 5 ) , 1973 (1966).  41.  R.T. Chen and D.E. Holmes, " D i s l o c a t i o n s t u d i e s i n 3 - i n c h diameter LEC GaAs", J . C r y s t a l Growth, 6 1 ( 1 ) , 111 (1983).  42.  W. Heinke and H.J. Q u e i s s e r , "Photoluminescence a t d i s l o c a t i o n s i n GaAs", Phys. Review L e t t . , 33(18), 1082 (1974).  43.  H. Emori, T. Matsumura, T. K i k u t a , and T. Fukuda, " E f f e c t o f ambient gas on undoped LEC GaAs c r y s t a l " , J a p n . J . A p p l . Phys., 22(11), 1652 (1983) .  44.  L.B. Ta, H.M. Hobgood, A. R h o t a g i , and R.N. Thomas, " E f f e c t s o f s t o i c h i o m e t r y on thermal s t a b i l i t y o f undoped, SI GaAs", J . A p p l . Phys., 5 3 ( 8 ) , 5771 (1982).  45.  D.E. Holmes, K.R. E l l i o t t , R.T. Chen and C.G. K i r k p a t r i c k , " S t o i c h i o m e t r y - r e l a t e d c e n t r e s i n LEC GaAs", P r o c . 2nd I n t . Conf. on SI III-V m a t e r i a l s ( E v i a n , F r a n c e ) , E d i t e d by S. Makram-Ebeid and B. Tuck, 19 (1982).  46.  K. Terashima, T. Katsumata, F. O r i t o , and T. Fukuda, " V e r t i c a l Magnetic f i e l d a p p l i e d LEC apparatus f o r l a r g e diameter GaAs s i n g l e c r y s t a l growth", Japn. J . A p p l . Phys., 2 3 ( 5 ) , L302 (1984).  47.  J . Osaka, H. Kohda, T. Kobayashi, and K. Hoshikawa, "Homogeneity o f v e r t i c a l magnetic f i e l d a p p l i e d LEC GaAs c r y s t a l " , Japn. J . A p p l . Phys., 2 3 ( 4 ) , LI95 (1984) .  48.  T. Shimada, K. Tereshima, H. Nakajima, and T. Fukuda, "Growth o f low and homogeneous d i s l o c a t i o n d e n i s t y GaAs c r y s t a l by improved LEC technique", Japn. J . A p p l . Phys., 2 3 ( 1 ) , L23 (1984).  49.  T. Shimida, T. Obakata, and T. Fukuda, "Growth and r e s i s t i v i t y c h a r a c t e r i s a t i o n o f undoped SI GaAs c r y s t a l s w i t h low d i s l o c a t i o n d e n s i t y " , Japn. J . A p p l . Phys., 2 3 ( 7 ) , L441 (1984).  50.  G. Jacob, M. Duseaux, J.P. Farges, M.M.B. Van Den Boom and P . J . Roksnoer, " D i s l o c a t i o n - f r e e GaAs and InP c r y s t a l s by i s o e l e c t r o n i c doping", J . C r y s t a l Growth, 61, 417 (1983).  51.  D.E. Holmes and R.T. Chen, "Contour maps o f EL2 deep l e v e l GaAs", J . A p p l . Phys., 55(10), 3588 (1984).  i n LEC  90  52.  G.M. M a r t i n , G. Jacob, G. P o r b l a n d , A. G o l t z e n e and C. Schwab", I d e n t i f i c a t i o n and a n a l y s i s of n e a r - i n f r a r e d a b s o r p t i o n band i n undoped and Cr-doped SI GaAs c r y s t a l s " , D e f e c t s and R a d i a t i o n E f f e c t s i n Semiconductors, R.R. H a s i g a t i e d i t o r , I n s t . Phys. Conf. s e r . 59, 281 (1981).  53.  M.R. B r o z e l , I . Grant, R.M. Ward, D.J. S t i r l a n d and M.S. S k o l n i c k , " D i r e c t o b s e r v a t i o n of f i n e s t r u c t u r e i n the c o n c e n t r a t i o n of the deep donor [EL2] and i t s c o r r e l a t i o n w i t h d i s l o c a t i o n s i n undoped, SI GaAs", J . A p p l . Phys., 5 6 ( 4 ) , 1109 (1984). T  54.  S. Miyazawa, T. M i z u t a n i , and H. Yamazaki, "Leakage c u r r e n t 1^ v a r i a t i o n c o r r e l a t e d w i t h d i s l o c a t i o n d e n s i t y i n undoped, SI LEC J a p n . J . A p p l . Phys., 2 1 ( 9 ) , L542 (1982 ) .  GaAs",  55.  T. Matsumura, H. Emori, K. Terashima, and T. Fukuda, " R e s i s t i v i t y , H a l l m o b i l i t y and leakage c u r r e n t v a r i a t i o n s i n undoped SI GaAs c r y s t a l grown by LEC method", Japn. J . A p p l . Phys., 2 2 ( 3 ) , L154 (1983).  56.  Y. Matsumoto and H. Watanabe, "Inhomogeneity i n SI GaAs r e v e a l e d by scanning leakage c u r r e n t measurements", Japn. J . A p p l . Phys., 3 2 ( 8 ) , L515 (1982).  57.  T. K i k u t a , K. Terashima, and K. I s h i d a , "Study of two d i f f e r e n t deep l e v e l s i n undoped LEC SI GaAs by photoluminescence s p e c t r o s c o p y " , J a p n . J . A p p l . Phys., 2 2 ( 7 ) , L409 (1983).  58.  I . Grant, D. Rumsby, R.M. Ware, M.R. B r o z e l , and B. Tuck, " E t c h p i t d e n s i t y , r e s i s t i v i t y and Cr d i s t r i b u t i o n i n Cr-doped LEC GaAs", P r o c . 2nd I n t . Conf. on SI III-V m a t e r i a l s ( E v i a n , F r a n c e ) , E d i t e d by S. Makram-Ebeid and B. Tuck, 99 (1982 ) .  59.  T. Honda, Y. I s h i i , S. Miyazawa, H.' Yamazaki, and Y. N a n i s h i , "The i n f l u e n c e of d i s l o c a t i o n d e n i s t y on the u n i f o r m i t y of e l e c t r i c a l p r o p e r t i e s of S i implanted SI LEC-GaAs", Japn. J . A p p l . Phys., 2 2 ( 5 ) , L270 (1983).  60.  R.T. B l u n t , S. C l a r k , and D.J. S t i r l a n d , " D i s l o c a t i o n d e n s i t y and sheet r e s i s t a n c e v a r i a t i o n a c r o s s SI GaAs wafers", IEEE T r a n s . E l e c t r o n D e v i c e s , 2 9 ( 7 ) , 1039 (1982).  61.  Y. N a n i s h i , S. I s h i d a , T. Honda, H. Yamazaki, and S. Miyazawa, "Inhomogeneous GaAs FET t h r e s h o l d v o l t a g e r e l a t e d to d i s l o c a t i o n d i s t r i b u t i o n " , Japn. J . A p p l . Phys., 2 1 ( 6 ) , L335 (1982).  62.  Y. N a n i s h i , S. I s h i d a , and S. Miyazawa, " C o r r e l a t i o n between d i s l o c a t i o n d i s t r i b u t i o n and FET performances observed i n low Cr doped LEC GaAs", Japn. J . A p p l . Phys., 2 2 ( 1 ) , L54 (1983).  63.  S. Miyazawa, Y. I s h i i ,  S. I s h i d a , and Y. N a n i s h i , " D i r e c t  91  o b s e r v a t i o n of d i s l o c a t i o n e f f e c t s on t h r e s h o l d v o l t a g e o f a GaAs FET", A p p l . Phys. L t t . 43(9), 853 (1983). 64.  S. Miyazawa and Y. I s h i i , " D i s l o c a t i o n s as the o r i g i n o f t h r e s h o l d v o l t a g e s c a t t e r i n g s f o r GaAs MESFET on LEC-grown semi- i n s u l a t i n g GaAs s u b s t r a t e " , IEEE Trans. E l e c t r o n D e v i c e s , 31(8), 1057 (1984).  65.  Y. I s h i i , S. Miyazawa, and S. I s h i d a , " T h r e s h o l d v o l t a g e s c a t t e r i n g o f GaAs MESFET's f a b r i c a t e d on LEC-grown s e m i - i n s u l a t i n g s u b s t r a t e s " , IEEE T r a n s . E l e c t r o n D e v i c e s , 31(6), 800 (1984).  66.  Y. I s h i i , S. Miyazawa, and S. I s h i d a , " C h a r a c t e r i z a t i o n o f t h i n a c t i v e l a y e r on s e m i - i n s u l a t i n g GaAs by mapping of FET a r r a y performance", IEEE Trans. E l e c t r o n D e v i c e s , 31 (8), 1051 (1984).  67.  H.V. Winston, A.T. Hunter, H.M. Olsen, R.P. Bryan, and R.E. Lee, "Substrate e f f e c t s on the t h r e s h o l d v o l t a g e of GaAs f i e l d - e f f e c t t r a n s i s t o r s " , A p p l . Phys. L e t t . , 4 5 ( 4 ) , 447 (1984).  68.  T.W. Hickmott, "Temperature dependence of FET p r o p e r t i e s f o r Cr-doped and LEC s e m i - i n s u l a t i n g GaAs s u b s t r a t e s " , IEEE T r a n s . E l e c t r o n D e v i c e s , 31(1), 54 (1984).  69.  T. I t o h and H. Y a n a i , " S t a b i l i t y of performance and i n t e r f a c i a l problems i n GaAs MESFET's", IEEE T r a n s . E l e c t r o n D e v i c e s , 2 7 ( 6 ) , 1037 (1980).  70.  C. Kocot and C.A. S t o l t e , "Backgating E l e c t r o n D e v i c e s , 2 9 ( 5 ) , 845 (1982).  71.  H. Goronkin, M.S. B i r r i t t e l l a , W.C. Seelbach, and R.L. V a i t k u s , "Backgating and l i g h t s e n s i t i v i t y i n i o n - i m p l a n t e d GaAs i n t e g r a t e d c i r c u i t s " , IEEE Trans. E l e c t r o n D e v i c e s , 2 9 ( 5 ) , 845 (1982).  72.  C P . Lee, S.J. Lee, and B.M. Welch, " C a r r i e r i n j e c t i o n and b a c k g a t i n g e f f e c t i n GaAs MESFET's", IEEE E l e c t r o n D e v i c e L e t t . , 3 ( 4 ) , 97 (1982 ) .  73.  T.H. M i e r s , W.M. P a u l s o n , and M.S. B i r r i t t e l l a , "The i n f l u e n c e of m a t e r i a l parameters on backgating i n GaAs i n t e g r a t e d c i r c u i t s " , GaAs and R e l a t e d Compounds, I n s t . Phys. Conf. s e r . 65, 339 (1982).  74.  N. Yokoyama, A. Shibatomi, S. Ohkawa, M. Fukuta, and H. Ishikawa, " E l e c t r i c a l p r o p e r t i e s o f the i n t e r f a c e between an n-GaAs e p i t a x i a l l a y e r and a Cr-doped s u b s t r a t e " , GaAs and R e l a t e d Compounds, I n s t . Phys. Conf. s e r . 33b, 201 (1976).  75.  T. I t o h and H. Y a n a i , " S t a b i l i t y of performance and i n t e r f a c i a l problems i n GaAs MESFET's", IEEE T r a n s . E l e c t r o n D e v i c e s , 2 7 ( 6 ) , 1037 (1980).  i n GaAs MESFET's", IEEE  Trans.  92  76.  M.S. B i r r i t t e l l a , W.C. Seelbach, and H. Goronkin, "The e f f e c t of b a c k g a t i n g on the d e s i g n and performance of GaAs d i g i t a l i n t e g r a t e d c i r c u i t s " , IEEE T r a n s . E l e c t r o n D e v i c e s , 29(7 ), 1135 (1982 ) .  77.  M.A. Lampert and P. Mark, C u r r e n t i n j e c t i o n s i n S o l i d s , New Academic P r e s s , 18 (1970).  78.  M.F. Chang, C P . Lee, L.D. Hou, R.P. Vahrenkamp, and C.G. K i r k p a t r i c k , "Mechanism of s u r f a c e c o n d u c t i o n i n s e m i - i n s u l a t i n g GaAs", A p p l . Phys. L e t t . , 4 4 ( 9 ) , 869 (1984) .  79.  D. D'Avanzo, "Proton i s o l a t i o n T r a n s . Microwave Theory Tech.,  80.  S. Makram-Ebeid, D. Gautard, P. D e v i l l a r d , and G.M. M a r t i n , " O u t d i f f u s i o n of the main e l e c t r o n t r a p i n bulk GaAs due to treatment", A p p l . Phys. L e t t . , 4 0 ( 2 ) , 161 (1982).  York:  f o r GaAs i n t e g r a t e d c i r c u i t s " , 30(7 ), 955 (1982).  IEEE  thermal  81.  G. T a r r and L. Young, F i r s t Annual r e p o r t f o r B r i t i s h C o u n c i l Grant #63A(RC-3), 5 (1982).  Columbia  Science  82.  M. Lau and L. Young, Second Annual r e p o r t f o r B r i t i s h C o u n c i l Grant #51 (RC-5 ) , 4 (1983).  Columbia  Science  .0  93  Appendix - Some deep l e v e l s i n SI GaAs r e p o r t e d i n the l i t e r a t u r e ( a d e t e c t e d by photocurrent-DLTS)  Author  E [eV] T  Capture Cross Section a [ cm ]  Association with trap classified by [3,4]  2  Martin et a l . [23]  F a i r m a n et a l . [22,24,32]  0.9 0.74 0.57 0.35 0.34 0.27  2 . 2 X 1 0  -  1  4  6.3xl0 5.4xl0 5.5xlO 2.7xl0 2.05xl0-  _ i 5  - i 3  - 1 5  - 1 4  0.9 2xl0" 0.83 2xl0 0.65(N)** l x l 0  il+  i l t  _ i 3  HL1 EL2 EL 3 EL 5 EL 6 HL12  Cr-doped Cr-doped Cr-doped Cr-doped Cr-doped Cr-doped  HL1 HL10  All* Cr-doped LEC GaAs All*  EL3 EL4 EL 6  Cr-doped LEC GaAs Cr-doped Bridgman GaAs All* VPE l a y e r on Cr-doped GaAs Cr-doped LEC & Bridgman GaAs Cr-doped Bridgman GaAs Cr-doped LEC GaAs VPE l a y e r on Cr-doped GaAs  - i 3  0.60 0.51(N)** 0.34 0.34 0.30 0.26 0.15 0.14  1x10" 1x10"-i 4xl06xl0~  1 2 2  1 1 + 1 3  7 X 1 0 -  1  1  lxl0-  HL12  *  2xl0"*  Material  2  i 6  Bridgman Bridgman Bridgman Bridgman Bridgman Bridgman  GaAs GaAs GaAs GaAs GaAs GaAs  * Cr-doped LEC & Bridgman GaAs and VPE l a y e r on Crdoped GaAs ** N e g a t i v e Peak as d i s c u s s e d i n s e c t i o n 3.4 HL1  Cr-doped Bridgman GaAs Cr-doped Bridgman GaAs  1 3  HL1  0.89 0.75 0.62  1.8xl0" 2.7xl0 1.5xl0 »  HL1 EL2 HL3  0.60  8.6xl0~  EL3  0.42 0.41  Not G i v e n 1.4xl0"15  n"-VPE l a y e r w i t h b u f f e r l a y e r on Cr-doped GaAs ri"-VPE l a y e r on Cr-doped GaAs n"-VPE l a y e r on Cr-doped GaAs ri"-VPE l a y e r w i t h b u f f e r l a y e r on Cr-doped GaAs ri"-VPE l a y e r w i t h and without b u f f e r l a y e r on Cr-doped GaAs n -VPE l a y e r on Cr-doped GaAs n~-VPE l a y e r w i t h b u f f e r l a y e r on CT-doped GaAs  Deveaud e t a l . [25]  0.87 0.5  2xl0 3xl0"  I t o h et a l • [26]  0.98  1.3xl0~  - 1 5  i 9  11+  - x l +  -1,  1 3  -  HL4  94 Author  E [eV] T  Capture Cross Section o [ cm ]  Association w i t h trap classified by [3,4]  2  Rhee e t a l . [27]  Yuba e t a l . [28]  0.90 0.85 0.73 0.17  2.1xl0 1.3xl0 1.3xl0~ 3.9xl0  0.88  5.5xl0~  0.86  1.2xl0  - i l  HL3  0.54  1.2xl0  - 1 3  EL 3  0.48  5.8xl0  - i l +  HL4  0.34  9.2xl0~  O l i v e r e t a l . 0.83 [30] 0.65(N) 0.57 0.34 0.28 0.15 H u r t e s et a l . 0.90 [21,31] 0.81  - 1 2  - 1 3  HLI  i 7  - 2 2  Not  1 3  i 3  Given  ELI  EL6  HL10  Cr-doped Cr-doped Cr-doped Cr-doped  GaAs GaAs GaAs GaAs  Cr-doped Bridgman b e f o r e and after S i implantation Cr-doped Bridgman a f t e r SI implantation Cr-doped Bridgman b e f o r e and after S i implantation Cr-doped Bridgman b e f o r e and after S i implantation Cr-doped Bridgman b e f o r e and after S i implantation undoped LEC GaAs grown w i t h  dry B 6  Not G i v e n Not Not Not Not  Material  undoped wet B undoped undoped undoped undoped  Given Given Given Given  Not G i v e n  HLI  Not  Given  EL 2  0.56  Not  Given  HL8  0.54  Not  Given  EL 3  0.41  Not  Given  HL4  0.32  Not  Given  EL 6  2  3  2  3  LEC 0 LEC LEC LEC LEC  GaAs grown w i t h GaAs GaAs GaAs GaAs  h i g h r e s i s t i v i t y VPE l a y e r on Cr-doped Bridgman n-VPE l a y e r w i t h h i g h r e s i s t i v i t y buffer layer on Cr-doped Bridgman h i g h r e s i s t i v i t y VPE b u f f e r l a y e r on Cr-doped Bridgman n-VPE l a y e r w i t h h i g h r e s i s t i v i t y b u f f e r l a y e r on Cr-doped Bridgman n-VPE l a y e r w i t h h i g h r e s i s t i v i t y b u f f e r l a y e r on Cr-doped Bridgman Both type o f samples  95  Author  E [eV] T  with trap classified by [3,4]  2  K. Lowe [3]  0.87 0.59 0.50 0.38 0.32  2.5xl0 5xl0 1.6xl0 3.2xl0 2.5xlO  Material  Association  Capture Cross Section a [ cm ] - 9  - i l  - l l f  _ i l +  _ i 3  ELI 2 EL4 EL 3 HL6 EL 8  undoped undoped undoped undoped undoped  LEC LEC LEC LEC LEC  GaAs GaAs GaAs GaAs GaAs  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0096300/manifest

Comment

Related Items