INTERDIFFUSION AND THERMALLY INDUCED STRAIN RELAXATION IN STRAINED SI1-XGEX/SI SUPERLATTICES

Thermal interdiffusion in five-period Si/Si1-xGex superlattices with periods of 200 angstrom 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 Si1-yGey 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-degrees-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 approximately 4. 0 eV was obtained. The elastic strain and the formation of crystal defects due to thermal treatment were investigated by He ion channeling.