Ion scattering studies of strained Si/Si1−xGex superlattices

Helium ion channeling and backscattering experiments have been performed on MBE-grown Si/Si_1−xGe_x superlattices to investigate interdiffusion, defect densities and tetragonal lattice distortion. Rapid Thermal Annealing (RTA) of these structures leads to substantial interdiffusion and strain relaxation. In some cases also relaxation by dislocation formation is observed after RTA, depending on the alloy composition x. Grazing incidence Rutherford backscattering spectroscopy was employed to observe the modulation of the backscattering yield of the superlattices. The modulation decreases due to interdiffusion after RTA. Interdiffusion coefficients were deduced for Ge concentrations between x=0.20 and x=0.70 in the temperature range between 900°C and 1125°C. The diffusivity increases with larger Ge concentrations. The activation energy for interdiffusion is 3.8 ± 0.2 eV.