Enhancement of zone-folding effects in the second order response of the [(Si)5/(Ge)5]/(Si0.4Ge0.6)(001) superlattice

We have carried out a full band structure calculation of the second harmonic generation (SHG) coefficient and the linear response function of a [(Si)5/(Ge)5] superlattice (SLS) on a Si0.4Ge0.6 alloy substrate. Our calculation gives the first indication of the magnitude, frequency dependence, and anisotropy of the second order response in this SLS. The ratio of the features due to zone-folded transitions to those due to bulk-like transitions is an order of magnitude larger than the same ratio in the linear response. Yet these zone-folded effects are still very small. Nonetheless, the overall size of the SHG coefficient for this SLS is slightly larger than that of the corresponding SLS on a Si(001) substrate.