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Based on the density functional theory with hybrid functional approach, we calculated the structural, electronic, and the optical properties of Cu2MgSn(S1-xSex)4 (CMTSSe), an potential photovoltaic material for thin film solar cells. The calculation reveals a phase transition from kesterite to stannite structure when Zn atoms are substituted by Mg atoms. In particular, the S-to-Se ratio can determine the energy splitting between the electronic states at the top of the valence band. The band gaps of CMTSSe can be tuned in the ranges of 1.01-1.58 eV. Calculated optical properties and tunable band gaps make them beneficial for achieving band-gap-graded solar cells.

The type-II InAs/GaSb superlattices (T2SLs)-based 640 × 512 long wavelength infrared (LWIR) Focal Plane Array (FPA) detector with15 μm pitch and 50% cut-off wavelength of 10.5 μm demonstrates a peak quantum efficiency of 38.6% and peak detectivity of 1.65 × 1011 cm Hz1/2 W−1 at 8.1 μm, high pixel operability of 99.5% and low responsivity non-uniformity of 2.69% at 80 K. The FPA exhibits clear infrared imaging at 110 K and diffusion-limited dark current densities below Tennant’s ‘Rule07’ at temperature above 100 K, which is attributed to the efficient suppression of diffusion dark current and surface leak current by introducing M-structure barrier and double hetero-structure passivation layers.

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.