FULL-BAND-STRUCTURE CALCULATION OF (EPSILON)2[--](OMEGA) AND (CHI)(2)[--](-2-OMEGA,OMEGA,OMEGA) FOR (GAAS)N/(GAP)N (N = 1,2) SUPERLATTICES ON GAAS(001) SUBSTRATES

We have carried out a full-band-structure calculation of the frequency-dependent dielectric tensor and second-harmonic-generation coefficient in (GaAs)n/(GaP)n (n = 1, 2) superlattices on GaAs(001) substrates. We use a linear combination of Gaussian orbitals technique, in conjunction with the X-alpha method for constructing the potentials of the constituent bulk materials, to calculate the electronic band structures and momentum matrix elements of these superlattices. The optical properties are then evaluated by utilizing a linearized tetrahedra sampling method. Our results indicate that the anisotropy in these materials is mostly due to tensile strain in the GaP layers. More importantly, in contrast to the (GaAs)n/(AlAs)n short-period superlattices, the effect of the strain here is to considerably enhance the second-harmonic response as compared with the average of the responses of the constituent bulk materials.