Second-Order Nonlinear Optical Properties of III-VI Semiconductor Monolayers from First-Principles Calculations

The family of III-VI semiconductors MX (M = Ga, In and X = S, Se) monolayers (MLs) has recently gotten attention as a new type of two dimensional materials for their significant electronic and optical properties such as layer dependent properties and sizable band gaps. In this thesis, a systematic first-principles study of second-order nonlinear optical properties of III-VI semiconductors was performed within density functional theory with local density approximation. The underlying determination of crystal structures was taken from experimental data. Our calculations with scissors corrections for bulk ε-GaSe and γ-InSe are in good agreement with experiment results, which shows that all MX MLs display significant second-order harmonic generation coefficients under scissors corrections. Furthermore, the prominent features in the χ(2)abc(−2ω, ω, ω) spectra for MX MLs are successfully correlated with the features in linear optical dielectric function ε(ω) in terms of single- and two-photon resonances. Among the MLs, InSe ML possesses the largest second-order harmonic generation susceptibility and the largest linear electro-optical coefficient