PHOTOLUMINESCENCE OF MBE GROWN SI1-CHIGE-CHI FILMS

The photoluminescence (PL) of MBE deposited Si1-xGex alloys has been measured over a range of temperatures (4.2-300 K) and x(0.10-0.78) thick epilayers (≥0.5 μm) on (100) silicon substrates. The PL was excited with laser light and the spectra were measured with a Fourier transform infrared spectrometer using a Ge photodiode detector. The spectra from relaxed films with low Ge concentrations contain silicon-like defect bands, substrate exciton lines, and a peak from alloy band-to-band recombination. The defect bands characterize the dislocations at the film-substrate interface. At higher germanium concentrations, the luminescence of the defect bands decreases in intensity and the band-to-band peak shifts to lower energy. The energy of this peak correlates with the bandgap energy measured by photoconductivity. Comparison is made with the PL from unrelaxed Si1-xGex epilayers and Si1-x/Si superlattices.