TYPE-II BAND ALIGNMENT IN SI1-XGEX SI(001) QUANTUM-WELLS - THE UBIQUITOUS TYPE-I LUMINESCENCE RESULTS FROM BAND BENDING/

We present experimental verification of type II band alignment in a co herently strained Si0.7Ge0.3/Si(001) quantum well by studying photolum inescence energy shifts under external strains. A recent determination of type I band alignment from a similar experiment is shown to result from band-bending effects due to high excitation. In high quality sam ples, the type II luminescence can be observed in the absence of exter nal stress by using extremely low excitation. The type II luminescence differs from the well known type I spectrum in a dramatic but as yet unexplained change in the relative intensities of the phonon replicas.