Influence of native defects on the infrared transmission of undoped Ga1−xInxSb bulk crystals

The below bandgap infrared transmission (up to 25 µm) in undoped Ga1−xInxSb bulk crystals has been studied for the first time and found to be limited by native defects such as antisites and vacancies found in antimonide-based III–V compounds. For the gallium-rich alloy compositions (x<0.5 in Ga1−xInxSb), the crystals exhibit p-type conductivity with an increase in net acceptor concentration and an increase in gallium content in the crystals. For x>0.5 (the indium-rich alloy compositions), the crystals exhibit n-type conductivity when the net donor concentration and indium content in the crystals increase. A correlation between the optical transmission and the residual carrier concentration arising from the native acceptors and donors has been observed. Due to donor-acceptor compensation, crystals with alloy compositions in the range of x=0.5−0.7 exhibit high optical transmission for a wide wavelength range (up to 22 µm). The light hole to heavy hole interband transition in the valence band and the free electron absorption in the conduction band have been found to be the two dominant absorption processes.