Ge-Si Atomic Layer Superlattices - A New Compound Semiconductor System

Ge-Si strained-layer superlattices have an electronic bandstructure very different from that of Ge or Si when the Superlattice period is less than 20 atomic monolayers. New interband optical transitions have been measured and confirmed through first principles calculations. Three important parameters: strains, periodicity and superlattice symmetry determining the spectrum of electronic states. In the case of a class of superlattice structures grown on Ge (001) superlattice, modulation spectroscopy and photoluminescence provide supporting evidence for the formation of a direct bandgap semiconductor.