Effects of strain on the band gap and effective mass in two-dimensional monolayer GaX (X = S, Se, Te)

Abstract

First-principles calculations have been performed to study the mechanical and electronic properties of two-dimensional monolayer GaX (X = S, Se, Te) under strain. It was found that the in-plane stiffness decreases from 86 N m⁻¹ for GaS and 68 N m⁻¹ for GaSe to 57 N m⁻¹ for GaTe, which is in good agreement with experimental results and is attributed to the weakening interactions between Ga and X atoms with the increasing atomic number of the X atoms. The band gaps of the GaX monolayers decrease approximately linearly with increasing tensile strain, while the variation in their band gaps with compressive strain does not show linearity, because the conduction band maximum is transferred among several high symmetry k-points. The effective masses of electrons and holes also exhibit strong anisotropy and can be modulated by applying both compressive and tensile strains, which indicates that monolayer GaX could be very useful for device modeling.