Microscopy of stress-induced morphological development and dislocation nucleation during semiconductor epitaxy

Abstract

Semiconductor films subjected to misfit stresses are unstable to the formation of surface undulations or waves. Atoms located in close proximity to the peaks of the undulations can relax and significantly lower the elastic energy of the film. Provided that the wavelength of the undulation is sufficiently large, this more than compensates for the associated increase in surface energy, leading to a morphological instability of the flat surface.An interesting feature of this instability is that although atomic planes near the peaks of the undulations can relax, stress concentrations develop at the undulation valleys. These stresses can be very large, even for rather shallow surface perturbations. The question, therefore, naturally arises as to the subsequent effect of these stresses on the evolving surface morphology and in particular, whether the magnitude of the stress is large enough to influence the nucleation of misfit dislocations. In order to study these issues experimentally, we have utilized Z-contrast imaging , atomic force microscopy (AFM), and plan-view transmission electron microscopy (TEM) to image the stress-induced surface evolution of SixGe1-x alloys which are compressively strained on Si(100).