VISIBLE PHOTOLUMINESCENCE FROM BIEXCITONS IN SI1-XGEX QUANTUM-WELLS

We have observed visible photoluminescence, at photon energies nearly twice those of the usual near-infrared excitonic emissions, from thin Si1-XGeX quantum wells at liquid He temperatures. This confirms that a significant biexciton population is present in such samples under exc itation conditions normally used for near-infared photo-luminescence m easurements. The intensity of the visible luminescence increases linea rly with excitation density, consistent with the biexcitons being loca lized by fluctuations in alloy content. The biexciton lifetime is obse rved to vary with the Si1-XGeX quantum well width indicating an enhanc ement of the overlap of the particle wave functions by the quantum con finement.