Processes limiting the performance of InAs/GaSb superlattice mid-infrared PIN mesa photodiodes

Abstract

In this study, we examine processes limiting the performance of 4 micron superlattice pin photodiodes for different temperature and mesa size regimes. We show that the performance of large mesa photodiodes at low temperature is most severely limited by a trap-assisted tunneling leakage current (x300), while small mesa sizes are additionally limited by perimeter leakage (x20). At room temperature, large mesa photodiodes are limited by the diffusion current, and small mesa photodiodes are further limited by the perimeter leakage (x100). To reduce or eliminate the impact of perimeter leakage, we have tried passivating the mesa sidewalls with SiN, an approach that was only minimally successful. We have also laid the groundwork for another approach to elimination of perimeter leakage currents, namely, elimination of the sidewalls altogether through planar processing techniques. Planar processing schemes require the deposition of a thick, wide bandgap semiconductor or "window layer" on top of the homojunction. We compare the performance of two otherwise identical InAs/GaSb superlattice homojunction detectors, except one with a GaSb window layer, and one without. We show that inclusion of the thick GaSb window layer does not degrade detector performance.