Surface Oxidation Doping to Enhance Photogenerated Carrier Separation Efficiency for Ultrahigh Gain Indium Selenide Photodetector

This work presents an ultrahigh gain InSe-based photodetector by using a novel approach called the surface oxidation doping (SOD) technique. The carrier concentration of multilayered two-dimensional (2D) InSe semiconductor surface has been modulated by controlling the formation of a surface oxide layer. The SOD through surface charge transfer at the interface of the oxide/2D InSe semiconductor heterostructure can lead to the creation of a vertical built-in potential and band bending as a result of the carrier concentration distribution gradient. The internal electric field caused by the formation of a carrier concentration gradient in InSe layers can facilitate charge separation of photogenerated electron hole pairs under light illumination. Consequently, the record high photoresponsivities of InSe-based photodetector with similar to 5 X 10(6) A/W at the excitation wavelength of 365 nm and 5 X 10(5) A/W at the wavelength of 530 nm can be obtained, outperforming the majority of photodetectors based on other 2D materials, such as graphene, MoS2, and even highly sensitive multilayer GaTe and In2Se3 flakes. The approach