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Epitaxial growth of dilute nitride-arsenide compound semiconductors by molecular beam epitaxy

University of British Columbia

In[sub y]Ga[sub 1-y]As[sub1-x]N[sub x] containing a small amount of nitrogen (x<0.05) is a new narrow bandgap semiconductor alloy that has advantageous properties for the fabrication of optoelectronic devices. In this thesis, we seek to improve the material quality of InGaAsN and GaAsN by studying how the epitaxial growth conditions affect both the structural and electronic properties of the alloy. We describe a novel RF plasma source based on a helical resonator design that was developed for the incorporation of nitrogen into GaAsN and InGaAsN thin films grown by molecular beam epitaxy. The plasma source is equipped with a baffle apparatus that decreases the ion content of the flux. We show how the structural and electronic properties of InGaAsN epilayers depend on the growth conditions. In situ light scattering measurements and atomic force microscopy show that a faceted surface morphology occurs when growth conditions increase adatom surface diffusion: slow growth rate, high substrate temperature and high V/III ratio. Large nitrogen concentrations also favour the faceted growth mode. The residual strain in relaxed InGaAsN films is found to be higher than in InGaAs epilayers having the same lattice mismatch. In situ substrate curvature measurements were used to monitor the strain state of. the sample in real time during the growth. Ex situ transmission electron microscopy and x-ray diffraction measurements agree with the residual strain determined with the in situ monitor. These characterization results also indicate that threading dislocation glide is slower in InGaAsN than in InGaAs. Finally, we find that the electronic properties of InGaAsN are generally degraded with increasing nitrogen content. However, by choosing appropriate growth conditions, we demonstrate InGaAsN quantum wells with room temperature photoluminescence efficiencies that are comparable to InGaAs structures. These photoluminescence results may be related to the faceting transition that was observed during GaAsN growth. In contrast with the findings of other groups, rapid thermal anneals only moderately improve the photoluminescence intensity and line shape of InGaAsN single quantum wells. We observe peak intensity gains on the order of 2 after one minute anneals at 785°C. Hall measurements indicate that the electron mobility of Si-doped GaAsN is inversely proportional to the nitrogen content. We conclude that nitrogen-related neutral impurity scattering is the limiting factor in the electron mobility of GaAsN. The use of Bi as a surfactant during growth is shown to improve the surface morphology of GaAsN epilayers and the photoluminescence properties of InGaAsN single quantum wells. This work provides insight into some of the key issues that must be taken into account in the growth of dilute nitrides.

Thesis/Dissertation

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2009-09-15

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http://hdl.handle.net/2429/12782

Astronomy

University of British Columbia

UBCV

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