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The Cu2ZnSnS4 (CZTS) thin films were fabricated by sulfurization of radiofrequency magnetron sputtered Cu–Zn–Sn–O (CZTO) precursors. Here, we extend recent works in the field of fabricating CZTO precursors by a new approach sputtering ZnO/Sn/Cu targets. The effects of one-step and two-step annealing processes applied for CZTO precursors on the structure, morphology, optical, and electrical properties were investigated systematically. The preannealing step of fundamental phase formation in the sulfurization process was also discussed. The two-step annealing process was found to affect the composition of element Sn slightly but significantly improved crystallinity, CZTS/Mo interfacial conditions, surface roughness, and electrical properties. The two-step annealed CZTS thin films had excellent optical and electrical properties with an optical band gap of 1.51 eV, a hole concentration of 2.4 × 1017 cm−3, and a hole mobility of 1.97 cm2/(V⋅s). In addition, the CZTS/Mo interface with small grains and voids were significantly improved. CZTS-based solar cell devices were successfully fabricated. The characteristics of current–voltage (J–V) curves indicated that short-circuit currents had a tendency to increase with the improvement of CZTS/Mo interface and surface morphology. As a result, the device based on two-step annealed CZTS thin films exhibited better performance with an open-circuit voltage of 553 mV, short-circuit current of 7.2 mA⋅cm−2, a fill factor of 37.8%, and a conversion efficiency of 1.51%.

The eight-band k ⋅ p model is used to establish the energy band structure model of the type-II InAs/GaSb superlattice detectors with a cut-off wavelength of 10.5 μm, and the best composition of M-structure in this type of device is calculated theoretically. In addition, we have also experimented on the devices designed with the best performance to investigate the effect of the active region p-type doping temperature on the quantum efficiency of the device. The results show that the modest active region doping temperature (Be: 760 °C) can improve the quantum efficiency of the device with the best performance, while excessive doping (Be: > 760 °C) is not conducive to improving the photo response. With the best designed structure and an appropriate doping concentration, a maximum quantum efficiency of 45% is achieved with a resistance–area product of 688 Ω ⋅cm2, corresponding to a maximum detectivity of 7.35 × 1011cm ⋅ Hz1/2/W.

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In this study, the etching and passivation processes of very long wavelength infrared (VLWIR) detector based on the InAs/GaSb/AlSb type-II superlattice has been studied. By studying the effect of each component in the citric acid solution (citric acid, phosphoric acid, hydrogen peroxide, deionized water), the best solution ratio is obtained. After comparing different passivation materials such as sulfide + SiO2, Al2O3, Si3N4 and SU8, it is found that SU8 passivation can reduce the dark current of the device to a greater degree. Combining this wet etching and SU8 passivation, the R0A of VLWIR detector with a mesa diameter of 500μm is about 3.6Ω·cm2 at 77K.

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