ALD-Al2O3 passivation effects on surface characteristics of InAs/GaSb type-II superlattice infrared photodetectors

To suppress the surface leakage current of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, atomic layer deposited (ALD)-Al₂O₃ passivation effects have been investigated. By using the ALD-Al₂O₃ passivation layers, surface leakage current was more effectively suppressed than by using chemical vapor deposited-SiO₂ passivation layers. The deposition temperature of ALD Al₂O₃ played an important role in minimizing the surface leakage current of T2SL infrared photodetectors. We found that the dark current density of mid-wavelength (MW) p-i-n structures was limited by their bulk components with Al₂O₃ passivation layers deposited at or below 200 °C, while the dark current density increased with the surface leakage when the layers were deposited at 260 °C. From the capacitance–voltage analysis, it was found that the deposition at 260 °C led to a large interface trap density at the Al₂O₃/GaSb interface. The results of X-ray photoelectron (XPS) spectroscopy show that the spectra of Sb₂O₃ decreases while that of Ga₂O₃ increases when the deposition temperature increases from 200 to 260 °C. This indicates that the reaction of Sb₂O₃ with GaSb is thermally enhanced. Based on these results, we conclude that Ga₂O₃ and/or elemental Sb may lead to an additional leakage path. Hence, suppression of the thermal decomposition of Sb-related oxides during Al₂O₃ deposition is required to obtain good passivation effects.