Mechanisms of strain induced roughening and dislocation multiplication in Si_xGe_1-x thin films

We discuss the stress driven roughening transition of Si_xGe_1-x thin films. In the case of annealed films, nucleation effects dominate the nature of the surface ripple which formed by a cooperative nucleation mechanism. Individual islands appear to nucleate via multilayer fluctuations. Faceting can however be suppressed at high supersaturations, resulting in a transition with characteristics of the Asaro-Tiller-Grinfeld instability. The relationship between morphological evolution and dislocation nucleation and multiplication is considered.