Defect-induced broadband photodetection of layered γ-In2Se3 nanofilm and its application in near infrared image sensors

In this study, we report on the synthesis of layered γ-In2Se3 for broadband photodetector and near infrared light image sensing applications. The layered γ-In2Se3 nanofilm with a thickness of around 74 nm was deposited onto a n-Si wafer through radio frequency magnetron sputtering. It is found that the as-assembled γ-In2Se3/n-Si shows an obvious photovoltaic behavior and can work properly as a self-powered broadband photodetector over a wide range of wavelengths (200–2200 nm). Such a unique spectral response beyond the absorption limit of both intrinsic γ-In2Se3 and n-Si can be ascribed to the existence of defect energy levels between the valence band and the conduction band, as a result of Se substitution of In atoms according to theoretical simulation based on first-principles calculations. Specifically, the γ-In2Se3/n-Si photodetector has a responsivity of 0.57 A W−1, a specific detectivity of 2.6 × 1012 Jones and a fast response speed (35/115 μs for τr/τf) under 808 nm light illumination, respectively, which are slightly better or comparable to other devices with similar geometries. Lastly, it was revealed that the γ-In2Se3/n-Si heterojunction photodetector can function as an effective near infrared (NIR) light image sensor with a decent spatial resolution, which suggests the great potential of the current device in future NIR optoelectronic systems.