NEAR-BAND-GAP PHOTOLUMINESCENCE OF SI1-XGEX ALLOYS GROWN ON SI(100) BY MOLECULAR-BEAM EPITAXY

Photoluminescence spectra in the near-band-gap region of Si 1-xGex alloys (x=0.04 and 0.15) grown on Si(100) substrates by molecular beam epitaxy have been measured at 4.2 and 12 K. Radiative recombinations of free and bound excitons in thin layers of Si 1-xGex alloys have been clearly observed for the first time. No-phonon transitions and transverse-optical (TO) phonon-assisted transitions have been identified. The luminescence lines become broader with an increase in excitation intensity; the broadening is interpreted to be due to the generation of the bound multiexciton complexes (BMECs). The position of the band-edge luminescence lines is determined by the strain in the epitaxial layer as well as the alloy composition. The defect-related L band appears in the case of x=0.15.