Avalanche photodetector in the GaSb/AlSb/InAs material system by molecular beam epitaxy

GaSb/AlSb/InAs is an attractive system for making low noise avalanche photodetectors (APD) due to possible resonant enhancement of hole impact ionization in Al_xGa_(1-x)Sb and potential enhancement of electron impact ionization in GaSb/AlSb superlattices. We have employed molecular beam epitaxy (MBE) to fabricate device structures so that these effects could be further explored. The devices were grown on GaSb substrates and incorporated a p^-n^+ one sided abrupt junction. The p^- multiplication region consisted of either bulk Al_(0.04)Ga_(0.96)Sb or 10 periods of alternating, 300 angstrom thick GaSb and AlSb layers. A short period, selectively doped InAs/AlSb superlattice was used as the n^+ layer. Dark current suppression in these devices was found to be largely dependent on the InAs/AlSb superlattice configuration and the resulting band offset at the p^-n^+ heterojunction. Notably, for devices with a 0.6 micrometer Al_(0.04)Ga_(0.96)Sb multiplication region and an optimized InAs/AlSb superlattice, an avalanche break down voltage of 13 V was observed. The dark current density for this device was 6 A/cm^2 at a multiplication factor of 10. Devices with GaSb/AlSb superlattice multiplication regions exhibited a higher breakdown voltage (18.5 V) and a lower dark current density (0.4 A/cm^2) at comparable gain. Impact ionization rates in Al_(0.04)Ga_(0.96)Sb were studied by using 781 nm and 1645 nm laser light. The results were consistent with enhancement of hole impact ionization in Al_(0.04)Ga_(0.96)Sb.