Near-band-gap photoluminescence of Si1−<i>x</i>Ge<i>x</i> alloys grown on Si(100) by molecular beam epitaxy

Abstract

Photoluminescence spectra in the near-band-gap region of Si1−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 Si1−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.