EXCITONIC PHOTOLUMINESCENCE FROM SI-CAPPED STRAINED SI1-XGEX LAYERS

High-quality fully strained Si1-xGex layers with 0% < x < 22% grown on Si(100) by rapid thermal chemical vapor deposition have been analyzed by photoluminescence spectroscopy. We report a well-resolved near-band-gap excitonic transition observed in SiGe layers. These transitions make it possible to determine directly the fundamental band gap of such strained Si1-xGex alloys. The results show that high surface recombination in very thin films prevents the observation of radiative recombination, while demonstrating the striking effectiveness of a Si epitaxial capping layer in eliminating surface recombination.