Spatially indirect radiative recombination of carriers localized in Si1-x-yGexCy/Si1-yCy double quantum well structure on Si substrates

Closely spaced pseudomorphic Si1-x-yGexCy and Si1-yCy quantum well (QW) layers grown by solid-source molecular beam epitaxy on Si substrates are studied by photoluminescence (PL) spectroscopy at low temperature. In thin Si0.84Ge0.16/Si1-yCy double QWs, a no-phonon PL line of enhanced intensity and a weaker Si-like TO-phonon replica line are observed at lower energy, compared to reference structures with isolated Si0.84Ge0.16 and Si1-yCy QWs. These PL lines are attributed to spatially indirect (type II) transitions of electrons and holes confined to the coupled Si1-yCy and Si1-xGex layers, respectively. The PL intensity depends strongly on layer width. It increases exponentially for decreasing QW widths and it decreases when thin Si layers are deposited in between the QWs. This behavior is well described considering the wave function overlap of carriers which strongly influences the rate of indirect optical transitions. (C) 1996 American Institute of Physics.