Strain relaxation in molecular beam epitaxially grown and compositionally graded epilayers on Si(001) at 750C was investigated by using high-resolution X-ray reciprocal space-mapping techniques. The depth profiles of residual strain and misfit dislocation density were compared with a theoretical model. It was shown that the lower parts of the graded films were completely or partially strain-relaxed, whereas the upper parts of the films remained fully strained with respect to the underlying relaxed part. It was concluded that the overall relaxation behavior of the graded film was in agreement with the Tersoff model. However, there was also an obvious quantitative discrepancy between the measured data and that model. The measured maximum residual strain was higher, than the prediction of the model, by a factor of about 2. Moreover, the partially relaxed inter-layer did not occur in the equilibrium model. It was suggested that such differences were caused by kinetic limitations to dislocation nucleation and propagation that were due to the growth temperature.

J.H.Li, V.Holy, G.Bauer, M.Hohnisch, H.J.Herzog, F.Schäffler: Journal of Crystal Growth, 1995, 157, 137-41