<i>Ab initio</i>study of the nonlinear optics of III-V semiconductors in the terahertz regime

Abstract

We compute from first principles the infrared dispersion of the nonlinear susceptibility ${\ensuremath{\chi}}^{(2)}$ in zinc-blende semiconductors. At terahertz frequencies the nonlinear susceptibility depends not only on the purely electronic response ${\ensuremath{\chi}}_{\ensuremath{\infty}}^{(2)}$, but also on three other parameters ${C}_{1}$, ${C}_{2}$, and ${C}_{3}$ describing the contributions from ionic motion. They relate to the TO Raman polarizability, the second-order displacement-induced dielectric polarization, and the third-order lattice potential. Contrary to previous theory, we find that mechanical anharmonicity $({C}_{3})$ dominates over electrical anharmonicity $({C}_{2})$, which is consistent with recent experiments on GaAs. We predict that the sharp minimum in the intensity of second-harmonic generation recently observed for GaAs between ${\ensuremath{\omega}}_{\mathrm{TO}}∕2$ and ${\ensuremath{\omega}}_{\mathrm{TO}}$ does not occur for several other III-V compounds.