Thermal degradation of the GaSb/AlOx interface associated with surface leakage in InAs/GaSb type-II superlattice infrared photodetectors

We systematically investigated the relationship between thermally induced interfacial degradation and mesa-sidewall leakage in InAs/GaSb type-II superlattice (T2SL) photodetectors passivated with atomic-layer-deposited AlOx (ALD-AlOx). Devices were passivated with 10 nm-thick ALD-AlOx deposited at 150, 200, and 260 °C and capped with a CVD-SiOx overlayer. Dark current density–voltage characteristics were measured at 80 K, and the surface-related contribution was evaluated from the perimeter-to-area (P/A) dependence of the dark current. Deposition at ≤200 °C resulted in low dark current with weak P/A dependence, whereas deposition at 260 °C produced substantially higher dark current with strong P/A dependence, indicating enhanced mesa-sidewall leakage. To investigate interfacial changes associated with this degradation, x-ray photoelectron spectroscopy was performed on 2 nm-thick AlOx deposited on InAs and GaSb substrates. The InAs/AlOx interface showed negligible temperature dependence, while the GaSb/AlOx interface exhibited significant compositional changes between 200 and 260 °C, including an increase in the Ga2O3 component accompanied by a decrease in the Sb2O3 component. Consistently, conductance-based C–V measurements of GaSb/AlOx metal-oxide-semiconductor capacitors revealed significantly increased interface trap density (Dit) values for deposition at 260 °C, particularly near the conduction band edge. Furthermore, post-deposition annealing at 260 °C enhanced both P/A-dependent leakage and an Sb-related Raman feature, consistent with thermally induced Sb-related chemical changes at the GaSb/AlOx interface. These results establish a systematic correlation among thermally induced chemical changes at the GaSb/AlOx interface, increased Dit, and enhanced mesa-sidewall leakage in T2SL photodetectors.