PHOTOLUMINESCENCE OF CONFINED EXCITONS IN MBE-GROWN SI1-XGEX/SI(100) SINGLE QUANTUM-WELLS

MBE-grown single quantum wells of pseudomorphic Si1-xGex/Si(100), with x = 21%, 24% and 36% and well widths L(z) from 1.2 nm to 250 nm were studied by photoluminescence using Fourier transform spectroscopy. Observations showed very low thermal deactivation energies of the luminescence, power-dependent luminescence intensities which vary with L(z) in a characteristic way, and power-dependent luminescence energy shifts, again showing characteristic L(z) dependence. Moreover, the TO-phonon sidebands were decomposed into their parent Si-Si, Si-Ge and Ge-Ge vibrations. These components exhibit relative strengths depending strongly on the optical power. All these data conspire to suggest Type II staggered band line-up in the Si1-xGex/Si heterojunction system for x less-than-or-equal-to 36%, whereas there is no easy explanation of the data by invoking a Type I band alignment.