Electronic structure and optical properties of short-period α-Sn_nGe_m superlattices

Short period α-Sn/Ge strained layer superlattices have been prepared on Ge(001) substrates by low temperature molecular beam epitaxy. We have achieved almost defect free and thermally stable single crystalline structures. Photourrent measurements in a series of Sn₁Ge_m(m>10) superlattices reveal a shift of the fundamental energy gap to smaller energies with decreasing Ge layer thickness m, in good agreement with band structure calculations. A direct fundamental energy gap and large direct band gap absorption is predicted for a slightly increased lateral lattice constant in α-Sn/Ge superlattices.