Theory of Low Energy Optical Transitions in Si/Ge Strained Layer Superlattices.

First, the optical transition energies for the strained layer superlattice Si sub 4 Ge sub 4 /Si(001) are calculated using the quasiparticle self energy approach and compared to available data. The type II alignment of the superlattice against the Si substrate is discussed in relation to the intensity of the low energy features in the electroreflectance spectra for this material. Then systematic trends for the direct/indirect absorption edge in the Si sub n Ge sub m series on Si(001) and Ge(001) substrates are evaluated based on a refined local empirical pseudopotential model.