Observation of Direct Band Gap Properties in Ge_nSi_m Strained-Layer Superlattices

Abstract

Photoluminescence and optical absorption measurements were carried out for Ge n Si m strained-layer superlattices grown by molecular beam epitaxy using a phase-locked epitaxy technique. A Ge 4 Si 12 superlattice showed intense emission in the near-infrared region, and its absorption coefficient followed the ( h v - E g ) 1/2 law, where h v is the energy of incident light and E g is the band gap energy. These results suggest that the Ge 4 Si 12 sample has a direct band gap.