High pressure photoluminescence studies of carbon-induced germanium quantum dots grown on Si

Abstract

We have performed photoluminescence (PL) investigations on a 0.2 monolayer C and a 0.2 monolayer C/1.84 monolayer Ge quantum dot (QD) structure sandwiched between Si layers. The dependence of the PL on hydrostatic pressure up to 12 GPa and laser excitation intensity ranging from 300 to 3000 W cm-2 has been studied at 10 K. The no-phonon PL peak and its transverse optic phonon replica in both the structures shift to low energies with increasing pressure. This indicates that the electrons are confined to the (2) conduction bands of Si in both these structures. With increasing laser excitation intensity, the PL transitions in the Si1-yCy quantum well remain at the same energy whereas a significant blue shift is seen in the energy of the no-phonon PL line and its transverse optic phonon replica in the carbon-induced Ge QDs. This behaviour is interpreted as evidence for type-I band alignment in the Si1-yCy quantum well and a staggered type-II band alignment in C-induced Ge QDs.