QUANTUM-CONFINED BIEXCITONS IN SI1-XGEX GROWN ON SI(001)

We report experimental evidence for the existence of three-dimensional ly (3D) -confined biexcitons in a strain-relaxed Si0.7Ge0.3 layer grow n on a stepwise graded buffer on Si(001) by ultrahigh vacuum chemical vapor deposition. A calculation of the photoluminescence line shape ba sed on a simple model is found to be in good agreement with experiment . From this theoretical fit we deduce a binding energy of 1.55 meV for the 3D-confined biexcitons. This binding energy is larger than the re ported value of 1.36 meV for a free biexciton in Si, indicating a quan tum-confinement effect.