Effective suppression of surface leakage currents in T2SL photodetectors with deep and vertical mesa sidewalls via TMA and H2 plasma combined pretreatment
For type-II InAs/GaSb superlattice (T2SL) photodetectors with deep and vertical mesa sidewalls, passivation for suppression of surface leakage currents is facing two key challenges that in the conformal coating of sharp sidewalls and increasing dominance of surface leakage currents as device dimensions shrink. In this work, atomic layer deposited (ALD)-Al2O3 and SiO2 method was employed as conformal passivation for deep and vertical mesa sidewalls. And a stable and high-quality interface between the ALD-Al2O3 and T2SL mesa sidewalls was obtained by the combined pretreatment of trimethylaluminum (TMA) and H2 plasma exposure (Al2O3TH), and thus a significant improvement in electrical performances has been achieved. The electrical performances before and after baking were compared among the Al2O3TH, conventional sulfur plus SiO2 passivated photodiodes. The dark current density of Al2O3TH passivated photodiodes were improved by 81% at 77 K under 0.1 V reverse bias and exhibited no deterioration after 90 °C-4 days baking treatment. Investigation on the effects of TMA and/or H2 plasma pretreatments demonstrates that combined pretreatment of TMA and H2 plasma, rather than TMA or H2 plasma alone, prior to the deposition of ALD-Al2O3 leads to a more thorough elimination of interface native oxides and surface states introduced in mesa process. The innovative application of this effective surface pretreatment technique is very encouraging for the passivation of deep and vertical sidewalls in III-V compound-based devices, such as large-format T2SL infrared detectors.