Second Harmonic Generation in GaAs-AlAs and Si-SiGe Quantum Well Structures

We present full scale relativistic pseudopotential calculations of both the first and second order susceptibility in p-type GaAs-AlAs and Si-SiGe structures. The frequency dependence of the linear and non-linear response due to transitions between valence mini-bands is calculated and the microscopic origin of the peaks determined. We show that simple particle-in-a-box models are unable to correctly describe the observed peak positions or the mechanisms involved. In particular, many important contributions come from areas of the Brillouin Zone away from the zone centre.