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 x 10(2) A.W-1 at 300 nm with an external quantum efficiency greater than 1.63 x 10(5) % at 5 V bias. The key figures-of-merit exceed that of graphene and other 20 material-based photodetectors reported to date. In addition, the photodetector has a fast response time of 1.8 x 10(-2) s and a specific detectivity of 2.26 x 10(12) Jones. The photoconductive response of alpha-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.