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

TL;DR

This study uses first-principles calculations to analyze the nonlinear optical response of III-V semiconductors in the terahertz range, revealing the dominance of mechanical anharmonicity and predicting material-specific behaviors.

Contribution

It provides a detailed ab-initio analysis of the nonlinear susceptibility in III-V semiconductors, highlighting the importance of ionic motion contributions and challenging previous assumptions about anharmonicity effects.

Findings

Mechanical anharmonicity ($C_3$) dominates over electrical anharmonicity ($C_2$).

The sharp minimum in second-harmonic generation intensity observed in GaAs does not occur in other III-V compounds.

The nonlinear susceptibility depends on both electronic and ionic contributions, with specific parameters identified.

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 $\chi^{(2)}_{\infty}$, 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 $\omega_{\rm TO}/2$ and $\omega_{\rm TO}$ does not occur for several other III-V compounds.