Defect-enhanced second-harmonic generation in (SimGen)p superlattices

Second-harmonic generation (SHG) has been applied to study the influence of defects in short-period (SimGen)p strained-layer superlattices. With a misfit stacking fault defect density of ∼1010 cm−2 shown by transmission electron microscopy, it is found that the SH intensity increases by about one order of magnitude from that of the defect-free samples. We propose that the inhomogeneous strain field around the fault planes in the superlattice layers is responsible for this abrupt increase of SHG. The expected symmetry and the magnitude of the nonlinear susceptibility from these stacking fault defects are shown to be in agreement with the experimental observations.