Nonlinear optics of III-V semiconductors in the terahertz regime: an ab-initio study

Abstract

We compute from first principles the infrared dispersion of the nonlinear susceptibility ${\chi }^{(2)}$ in zincblende semiconductors. At terahertz frequencies the nonlinear susceptibility depends not only on the purely electronic response ${\chi }_{\infty }^{(2)}$, 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 ${\omega }_{\mathrm{TO}}/2$ and ${\omega }_{\mathrm{TO}}$ does not occur for several other III-V compounds.

9 pages, 3 figures; updated bibliography