Electro- and Photoreflectance of Ultrathin Ge/Si Superlattices Grown by Phase-Locked Epitaxy

Abstract

Optical studies of ultrathin Ge/Si superlattices grown on (001) Si substrates by phase-locked epitaxy have been carried out. The structures consist of alternating layers of pure Ge and Si with periods of 8, 10 and 12 monolayers. Using photo- and electroreflectance (PR and ER), four structurally induced optical transitions have been observed in the energy ragion 0.76–2.5 eV in both systems with periods of 8 and 10 monolayers. The transition energies show a blue shift with decreasing strain. At a growth temperature of 400°C, the PR and ER spectra of Ge 6 /Si 6 , which has a period of 12 monolayers, show not alloylike behavior but superlattice features similar to the samples with periods of 8 and 10 monolayers.