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Microscopic origin of optical nonlinearities associated with excitations between valence minibands in p-type GaAs-AlAs and Si-Si1-xGex heterostructures.

We have carried out full-scale semi-empirical relativistic pseudopotential calculations of the frequency dependence-spanning the midinfrared to far infrared range of frequencies-of χ (2) (-2ω; ω, ω) associated with excitations between valence minibands in p-type GaAs-AlAs and Si-SiGe heterostructures. We find that the spectrum is dominated by excitations lying further from the center of the Brillouin zone and depends on states lying above the semiclassical barrier