Second-Harmonic Generation in GaAs: Experiment versus Theoretical Predictions ofχxyz(2)

For GaAs we have determined $|{\chi }_{xyz}^{(2)}(-2\omega ;\omega ,\omega )|$ in second-harmonic generation experiments using two-photon energies between 2 and 5 eV. In addition to the $E_1$, $E_1+{\Delta }_1$, $E_0^{\prime }$, and $E_2$ critical-point bulk transitions of GaAs, a surprisingly strong surface transition at 3.35 eV was observed for natively oxidized GaAs(001) samples. A detailed comparison with theoretical predictions reveals that calculations that include many-particle effects at the level of the “scissors” approximation can describe the overall frequency dependence of the second-harmonic susceptibility reasonably well.