Ion scattering studies of diffusion and strain relaxation in Si/Si1-xGex superlattices

Rutherford backscattering (RBS) and ion channeling experiments have been performed on MBE-grown Si/Si1-xGex superlattices with a period length of 20 nm to investigate interdiffusion, defect densities and tetragonal lattice distortion. Rapid thermal annealing (RTA) in the temperature range between 900 and 1125degC leads to substantial interdiffusion. Grazing incidence Rutherford backscattering spectroscopy shows clearly a decrase of the amplitudes of the modulations of the backscattering yield due to interdiffusion. Interdiffusion coefficients were deduced for different superlattices with Ge concentrations between x=0.20 and x=0.70. The interdiffusivity increases for higher Ge concentrations. An average activation energy of 3.8±0.2 eV for interdiffusion has been obtained. Strain and strain relaxation by dislocation formation seem to have no measurable effect on the activation energy. (orig.)