Dislocation motion in strained thin films. Are Kinks colliding with each other?

For epi-threading dislocations in Si0.9Ge0.1 strained epitaxial films grown on Si, the velocity of their lateral propagation parallel to the hetero-interface is found to increase almost linearly with film thickness h and exhibits saturation above h ≈︁ 700 nm, while the activation energy is invariable over the thickness range investigated. The thickness-dependent velocity cannot be explained quantitatively by the inevitable effect of line tension due to interfacial dislocations which whould reduce the velocity of epi-threading dislocations at small thicknesses. The invariable activation energy contradicts another conceivable interpretation considering transition in the glide mode, with increasing dislocation length, from the no-kink-collision regime to the kink-collision regime. Paradoxical facts including the present one are well accounted for by a new model supposing the presence of obstacles on dislocations which effectively limits the kink mean free path to a shorter distance than that determined by kink collision.