Strain and electric field-modulated indirect-to-direct band transition of monolayer GaInS2

The strain- and electric field-dependent electronic and optical properties of monolayer GaInS(2 )have been calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT) GaInS2 monolayer shows an indirect band gap of 1.79 eV where valence band maxima (VBM) and conduction band maxima (CBM) rest between the K and Gamma point and at the Gamma point, respectively, while at 4% compressive strain, the material changes from indirect to direct band gap of 2.22 eV having the VBM and CBM at the Gamma point. With a further increase in compressive strain, the CBM shifts, from the Gamma to the M point, which leads to an indirect band gap again. The electric field also affects the band structure of monolayer GaInS2 and shifts the transition from direct to indirect band gap at a positive electric field of 4 V/nm, which acts normal to the surface. The strain-dependent optical properties are also calculated, which suggests that the absorption coefficient increases with compressive strain. Our work demonstrates a wide range of band gap variation and optical properties improvement upon application of biaxial strain and electric field on the monolayer of GaInS2.