  In a semiconductor heterostructure with type II energy band alignment, the
spatial separation between electrons and holes slows down their radiative
recombination. With increasing excitation intensity, Auger recombination
quickly becomes the dominate recombination channel, and it produces carrier
ejection from the quantum well. Here, we show that in Si/SiGe three-dimensional
nanostructures, this efficient process facilitates the formation of an
electron-hole plasma (EHP) and/or electron-hole droplets (EHDs) in thin Si
barriers separating SiGe clusters. In contrast to conventional, strongly
temperature dependent and slow radiative carrier recombination in bulk Si, this
EHD/EHP luminescence in nanometer-thick Si layers is found to be nearly
temperature independent with radiative lifetime approaching 10^-8 s, which is
only slightly slower than that found in direct band gap III-V semiconductors.
