THE NEAR-INFRARED PHOTOLUMINESCENCE OF GAAS EPILAYERS GROWN ON SI

In heteroepitaxial GaAs grown on Si (GaAs/Si) there exist deep levels caused by various charged states of defects because of large lattice m isfit and thermal expansion mismatch between GaAs and Si. The temperat ure-and excitation intensity-dependent near-infrared photoluminescence spectra related to the deep levels present in GaAs/Si grown by metal- organic chemical vapour deposition with different ratios of [As]/[Ga] were studied. In terms of configuration coordinate model, the Franck-C ondon shifts of near-infrared emission in GaAs/Si were obtained by mea suring the variation in full width at half-maximum with temperature. T he band-gap shifts with temperature and with mismatch strain in GaAs/S i were considered. Taking Franck-Condon and band-gap shifts into accou nt, the energy relations for the transitions from donor to acceptor, f rom conduction band to acceptor and from donor to valence band were re vised. According to these transition-energy relations and the emission characteristics of GaAs/Si epilayers, three emissions were interprete d as the recombination luminescence of donor-acceptor pairs and two em issions were caused by As interstitial-Ga vacancy complex centres.