Interdiffusion and thermally induced strain relaxation in strained ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$/Si superlattices

Thermal interdiffusion in five-period Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ superlattices with periods of 200 Å and Ge concentrations between x=0.20 and 0.70 was studied using Rutherford backscattering spectrometry in grazing-angle geometry. Both asymmetrically strained superlattices grown directly on Si, as well as symmetrically strained superlattices grown on relaxed ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ ${\mathrm{Ge}}_{\mathit{y}}$ buffer layers, were grown to compare the influence of the strain distribution on the interdiffusion. Rapid thermal annealing in the temperature range between 900 and 1125 °C leads to substantial interdiffusion indicated by a significant decrease of the amplitudes of the modulations of the backscattering yield. Interdiffusion coefficients were deduced using a Fourier algorithm. For a given Ge concentration x, the thermal dependence of the interdiffusion coefficients follows an Arrhenius law. The interdiffusivity increases with increasing Ge concentrations. An average activation energy for interdiffusion of ∼4.0 eV was obtained. The elastic strain and the formation of crystal defects due to thermal treatment were investigated by He ion channeling.