Two-dimensional GeAs with a visible range band gap

Abstract

Two-dimensional (2D) layered structures have recently drawn worldwide attention because of their intriguing optical and electrical properties. In this study, we prepared GeAs nanosheets as a new 2D material by a liquid-phase exfoliation method. The few-layered nanosheets had a band gap close to 2.1 eV, which is significantly higher (by about 1.5 eV) compared to the bulk. The value of 2.1 eV is in excellent agreement with that for the monolayer obtained from first-principles (HSE-06) calculations; mono-, bi-, tri-, and tetra-layers have remarkable direct or quasi-direct band gaps of 2.125, 1.339, 1.112, and 1.017 eV, respectively. The electrical properties of individual GeAs nanosheets were measured to reveal their 2D carrier transport behaviors. We also observed stable and large photocurrents, indicating potential application in high-performance optoelectronic nanodevices. The few-layered GeAs nanosheets deposited on n-type Si nanowire arrays showed promising photoelectrochemical water splitting under visible light irradiation. Band alignment based on the calculated band edge positions suggested a buildup of the space charge region in the p-GeAs/n-Si heterojunction, as well as the band bending of n-Si at the electrolyte interface.