Performance Improvement of Molecular Beam Epitaxy Grown InSb Photodiodes for Room Temperature Operation

In this paper, we report the optimization of the light absorber layer thickness of InSb p+–p-–n+ photodiodes grown by molecular beam epitaxy (MBE) on GaAs(001) substrates. An Al0.17In0.83Sb barrier layer between p+ and p- layers was used to reduce the diffusion of photoexcited electrons, allowing rectifying characteristics and high photovoltage response at room temperature. Photodiodes with a junction area of 90×90 µm2 and p--layer thicknesses varying from 0.5 to 3 µm were fabricated, demonstrating that photocurrent increased with p--layer thickness, which is in good agreement with theoretical calculations. However, the non biased differential resistance did not increase as expected, possibly owing to an increase in film defect density with increasing film thickness, which is considered to produce leakage paths through the light absorber layer. Despite the presence of defects on the grown films, photodiodes with a p--layer thickness of 3 µm showed a sixfold improvement in the signal-to-noise ratio when compared with that of 0.5 µm.