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Optical and electronic properties of GaAsBi alloys for device applications

University of British Columbia

GaAs1-xBix is a new III-V semiconductor alloy that shows promise for many optoelectronic applications. In this thesis, several characterization techniques were used to explore the properties of molecular beam epitaxy grown GaAs1-xBix alloys in a wide range of Bi-content. The fundamental bandgap and the optical absorption coefficient of pseudomorphic GaAs1-xBix/GaAs films are studied by optical transmission and photoluminescence spectroscopies. All GaAs1-xBix films (0≤x≤17.8%) show direct optical bandgaps. The bandgap (Eg) decreases strongly with increasing Bi-content, reaching 0.52 eV (~2.4 µm) at 17.8% Bi. At Eg <1.06 eV, GaAs1-xBix has the least lattice mismatch from GaAs of any ternary GaAs alloy, including GaAsN, for a given bandgap. Below the GaAs1-xBix bandgap, exponential absorption tails are observed with Urbach energies 3-6× larger than that of bulk GaAs. The electrical conductivity and Hall transport measurements on nominally undoped GaAs1-xBix films with 0<x≤21.5% Bi reveal an exponential increase in p-type conductivity and a monotonic decrease in hole mobility with increasing Bi-content. From temperature dependent electrical measurements, this behavior is found to be associated with an increase in the density of states in the valence band of GaAs1-xBix alloys and the presence of Bi-induced acceptor states above the valence band. A few optoelectronic device applications of GaAs1-xBix alloys are also examined in this thesis. The photovoltaic response of single junction dilute GaAs1−xBix p+/n diodes were investigated for the first time. With the introduction of Bi into GaAs, the spectral response is shown to expand to longer wavelengths than in GaAs. Based on theoretical modeling, the minority carrier lifetimes in unoptimized bismide material are found to be significantly shorter than the standard grown GaAs, resulting in low collection efficiency in solar cell devices. Furthermore, a systematic analysis is carried out to investigate the influence of rapid thermal annealing on the terahertz emission from bismide based photoconductive switches. Notable enhancement in terms of terahertz emission amplitude and bandwidth are demonstrated from annealed GaAs1-xBix substrates. The optimum thermal annealing was found at 670 °C and 1 min duration. We found that GaAs1-xBix can perform better than conventional low temperature GaAs in generating the terahertz radiation.

Text

2015-08-20

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54559

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/