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 excitation conditions normally used for near-infared photo-luminescence measurements. The intensity of the visible luminescence increases linearly with excitation density, consistent with the biexcitons being localized by fluctuations in alloy content. The biexciton lifetime is observed to vary with the Si1-XGeX quantum well width indicating an enhancement of the overlap of the particle wave functions by the quantum confinement.