First-Principles Study of Monolayer GeTe and the Effect of External Strain and Electric Field

The electronic properties of hexagonal and d-NaCl structure of monolayer GeTe, as well as the effect of external biaxial strain and electric field, were studied by first-principles calculations. The calculated binding energy theoretically indicated a slightly greater possibility of forming two-dimensional (2D) GeTe with a d-NaCl structure. The band structures of d-NaCl monolayer GeTe were dramatically transformed from semiconductor to metallic under a compressive biaxial strain and a positive electric field. The hexagonal monolayer GeTe demonstrated potential for photocatalytic water splitting due to its suitable band edge positions. In addition, it was possible to tune the band edge positions by the external biaxial strain and electric field to improve the photocatalytic efficiency. The H₂O-gas sensing properties of monolayer GeTe and the inner mechanisms of charge transfer were investigated. In the case of H₂O-adsorbed Ge-top hexagonal monolayer GeTe, the charge transfer reached 0.056 e under compressive strain of −4%, which is significantly greater than that for most other 2D materials.