The residual strains which followed relaxation in various SiGe hetero-epitaxial films, grown on (001)Si wafers, were compared with the values of residual strain which were predicted by a theory that was based upon the incremental movements of isolated threading dislocation segments. It was found that, for very thin films (40 to 500nm), the measured residual strains after relaxation were significantly higher that the values which were predicted by theory. In the case of thicker films, the residual strains were very close to the predicted values. The effect, upon residual strains, of the interactions of parallel dislocations were investigated by using a model that had been developed for a 2-dimensional array of dislocations. It was found that the experimental data could not be explained by this model since it predicted even lower values of residual strain then did a model which was based upon isolated threading segments. The residual strains were also compared with predictions that were based upon Freund’s treatment of the blocking of a moving threading segment by an orthogonal misfit dislocation in its path. It was found that Freund’s blocking criterion gave a very good account of the residual strain in the SiGe films. The blocking of threading dislocations by other misfit dislocations appeared to play an important role in the later stages of strain relaxation in these structures, and could therefore reduce the possibility of obtaining fully relaxed films with low threading dislocation densities.

V.T.Gillard, W.D.Nix, L.B.Freund: Journal of Applied Physics, 1994, 76[11], 7280-7