Electronic and optical properties of two-dimensional InSe from a DFT-parametrized tight-binding model

We present a tight-binding (TB) model and k·p theory for electrons in monolayer and few-layer InSe. The model is constructed from a basis of all s and p valence orbitals on both indium and selenium atoms, with tight-binding parameters obtained from fitting to independently computed density functional theory (DFT) band structures for mono- and bilayer InSe. For the valence and conduction band edges of few-layer InSe, which appear to be in the vicinity of the Γ point, we calculate the absorption coefficient for the principal optical transitions as a function of the number of layers, N. We find a strong dependence on N of the principal optical transition energies, selection rules, and optical oscillation strengths, in agreement with recent observations [D. A. Bandurin et al., Nat. Nanotechnol. (2016)]. Also, we find that the conduction band electrons are relatively light (m∝0.14--0.18mₑ), in contrast to an almost flat, and slightly inverted, dispersion of valence band holes near the Γ point, which is found for up to N∝6.