Low temperature photoluminescence in ultra-thin germanium quantum wells

We measured the photoluminescence (PL) spectra of a series of Ge n quantum wells as a function of temperature, from 2K to 50K. The PL spectra at 2.1K are dominated by broad emission lines, which can be interpreted as recombination across the indirect gap of the Si/Ge microstructure and are strongly influenced by the interface morphology of each sample. Beyond T 15K, all samples show identical spectra in which the broad structures are replaced by thin, strong lines. We interpret these changes as a quenching of the recpmbination across the gap PL of the microstructure and the appearance of defect-related peaks from the Si substrate