Enhancement in below bandgap room temperature infrared transmission has been observed in tellurium (Te)-doped GaSb bulk crystals. The effect of Te concentration on the transmission characteristics of GaSb has been experimentally and theoretically analysed. Undoped GaSb is known to exhibit p-type conductivity with residual hole concentration of the order of (1-2) × 10 17 cm −3 at room temperature due to the formation of native defects. For such samples, inter-valence band absorption has been found to be the dominant absorption mechanism. The residual holes could be compensated by n-type dopants such as Te. With increasing Te concentration, free carrier absorption due to electrons and inter-valley transitions in the conduction subband become significant. The dependences of various absorption mechanisms as a function of wavelength have been discussed in this paper.

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A cadmium sulfide thin film deposited by a chemical bath deposition technique has been found to act as a passivating layer and a capping layer for GaSb photodiodes. X-ray photoelectron spectroscopy analysis shows the presence of Ga–S and Sb–S bonds along with the cadmium binding energies. Reduction in the reverse leakage current after the passivation is accompanied by a significant increase in the zero bias resistance-area product (14.29–100Ωcm2). In addition, the dependence of the zero bias resistance-area product on the device dimension reduced considerably. There was no degradation in the dark current performance over a period of 3months, indicating long-term stability.

The below band-gap optical-absorption characteristics of GaxIn1−xSb alloy system have been reported. The different dependencies of the hole and electron absorption mechanisms on wavelength result in significant changes of the absorption characteristics with alloy composition. In the undoped Ga-rich alloy compositions that are p type in nature (due to residual holes resulting from native defects), the inter-valence-band absorption has been found to be the dominant absorption mechanism. With decreasing Ga (increasing indium) mole fraction, the hole to electron ratio decreases for undoped samples. For such samples, absorption due to electrons becomes significant. With n-type extrinsic doping, intervalley transitions are seen for certain Ga-rich compositions, which also alter the absorption characteristics. The dependencies of various absorption mechanisms as a function of wavelength have been analyzed and discussed in this paper. Based on the theoretical analysis presented in this paper, one can calculate the extrinsic doping level necessary for each alloy composition in order to obtain high optical transparency necessary for infrared optical applications.

This paper presents two of our recent developments in the area of III-V ternary and quaternary materials growth technology for high efficiency thermophotovoltaic (TPV) cells. It is well recognized that growth of TPV cell materials from melts or solutions presents the most economical option. We have investigated bulk substrate growth from melt as well as epitaxial growth from liquid phase. In the bulk crystal growth area, we have been concentrating on the growth of 50 mm or larger diameter device quality ternary III-V substrates. In the epitaxial growth arena, we have developed a new thermochemistry for growing ternary and quaternary compounds on binary substrates from quaternary solutions. Some of the recent results pertaining to the bulk growth of GaInSb and epitaxial growth of GaInAs, InAsSb and GaInAsSb on GaAs substrates will be discussed here.