RESONANT 2ND-HARMONIC GENERATION IN TYPE-II HETEROSTRUCTURES OF INP AL(0.48)IN(0.52)AS/

We report an experimental study of the second-harmonic generation in a type-II InP/Al0.48In0.52As heterostructure at frequencies of the fund amental beam resonant with the spatially indirect-band-gap transitions . From the comparison between the second-harmonic spectrum of the hete rostructure and that of an InP crystal in the region 1.15-1.45 eV, we show an enhancement of the second-order susceptibility in the former t hat is related to the transitions between electron- and hole-confined states. From a study of the dependence of the second-harmonic generati on on the polarization directions and the sample orientation, the symm etry properties of the second-harmonic tenser have been derived. These correspond to a T-d (bulklike) symmetry class and the data show the p redominance, in the visible region, of the contributions to the second -order nonlinear susceptibility coming from transitions involving high -energy nonconfined states. The terms of lower symmetry involving only low-energy confined states give in this case a negligible contributio n.