Defects in GaAs after Si indiffusion and annealing: A TEM and CL study

Silicon diffusion was carried out from a thin (50 nm) sputtered film into undoped semi-insulating and Te- or Zn-doped LEC-GaAs at 900 °C for 5 h under various As pressures. Secondary ion mass spectroscopy and spreading resistance technique were used to characterize the Si indiffusion profiles. Lattice defects in highly Si-doped diffusion region were examined as a function of post-diffusion heat treatments (first at 700 °C for 15 min and second at 1000 °C for 30 min) by using transmission electron microscopy of plan-view and cross-sectional samples. Two types of defect were observed in the diffusion region: (i) perfect prismatic loops on {110} planes and of the interstitial type and (ii) Frank faulted loops on {111} planes, also of the interstitial type. A model for the defect formation and the role of Si in the defect generation are discussed in terms of a negative temperature dependence of thermal equilibrium concentrations of VGa3−, which are assumed to mediate the Si diffusion under high n-doping conditions. Cathodoluminescence spectra measured at 4 K and 77 K were obtained from the diffusion layer. Si diffusion affects the band-gap luminescence and generates two deep-level emission bands in the 0.9–1.3 eV spectral region. It is suggested that these deep levels are associated with some diffusion-induced defects and defect complexes.