INFRARED OPTICAL-PROPERTIES AND BAND-STRUCTURE OF A-SN/GE SUPERLATTICES ON GE SUBSTRATES

Short-period alpha-Sn/Ge strained-layer superlattices have been prepared on [001] Ge substrates by low-temperature molecular-beam epitaxy. We have achieved almost-defect-free and thermally stable single-crystalline structures. Photocurrent 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 is predicted for a slightly increased lateral lattice constant in alpha-Sn/Ge superlattices.