Second-harmonic generation in GaAs: experiment versus theoretical predictions of chi(2)xyz.

For GaAs we have determined |chi((2))(xyz)(-2omega;omega,omega)| in second-harmonic generation experiments using two-photon energies between 2 and 5 eV. In addition to the E1, E1+delta(1), E'0, and E2 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.