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 ∼5 × 10⁶ A/W at the excitation wavelength of 365 nm and 5 × 10⁵ 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 based on SOD induced efficient photogenerated charge separation can be also applied to other 2D layered semiconductors.