Engineering of electronic and optical properties of monolayer gallium sulfide/selenide in presence of intrinsic atomic defects

Abstract

In this paper, the electronic and optical properties of various point defects in gallium sulfide (GaS) and gallium selenide (GaSe) are studied. Various vacancy defects in each monolayer GaX (X = S, Se) include VX, VGa, 2VX, 2VGa, 1VGa1VX, 1VGa2VX, 2VGa1VX, 2VGa2VX. We compute the band structure, zero-bias transmission spectrum, and dielectric function for all considered structures. The calculations are carried out by the first-principles method. The calculation results indicate that the absence of S/Se atom in these semiconductors leads to the transition from an indirect band gap for the pristine materials to a direct band gap in their defective systems and the band gap energies change from 2.3 eV/2.11 eV to 1.33 eV/0.98 eV, respectively. Also, 2VX causes that the semiconductor band gap changes from indirect to direct. Furthermore, GaX monolayer is converted to a p-type semiconductor in the presence of VGa. Moreover, these findings represent that some of the point defects in this system lead to magnetic states which can be employed in spintronic devices. In addition, for the defective GaX monolayers with the direct band gap, the first peak of imaginary part of the dielectric function occurs around their band gap energy. The study of intrinsic structural defects in monolayer GaX provides new opportunities for optimizing the electronic and optical properties of these materials via defect engineering.