Extraordinary Photoresponse in Two-Dimensional In₂Se₃ Nanosheets

We demonstrate extraordinary photoconductive behavior in two-dimensional (2D) crystalline indium selenide (In₂Se₃) nanosheets. Photocurrent measurements reveal that semiconducting In₂Se₃ nanosheets have an extremely high response to visible light, exhibiting a photoresponsivity of 3.95 × 10² A·W^–1 at 300 nm with an external quantum efficiency greater than 1.63 × 10⁵ % at 5 V bias. The key figures-of-merit exceed that of graphene and other 2D material-based photodetectors reported to date. In addition, the photodetector has a fast response time of 1.8 × 10^–2 s and a specific detectivity of 2.26 × 10¹² Jones. The photoconductive response of α-In₂Se₃ nanosheets extends into ultraviolet, visible, and near-infrared spectral regions. The high photocurrent response is attributed to the direct band gap (E_G = 1.3 eV) of In₂Se₃ combined with a large surface-area-to-volume ratio and a self-terminated/native-oxide-free surface, which help to reduce carrier recombination while keeping fast response, allowing for real-time detection under very low-light conditions.