Stress and Temperature Dependence of Misfit Dislocation Nucleation Rate in SiGe Alloys: Evidence of Homogeneous Nucleation

Abstract

AbstractA recent theory on the brittle-to-ductile transition (BDT) sheds new light on the issue of the generation of misfit dislocations- in strained epitaxial layers. The Khantha-Pope-Vitek model of the BDT states that thermal fluctuations in the lattice, assisted by an applied stress, can result in the spontaneous generation of dislocations. Application of the KPV model to the problem of epitaxial layers predicts that at a critical temperature and stress, a sudden onset of homogeneous islocation generation will occur.In this paper the dislocation nucleation rate in SiGe strained layers of varying isfit stress is investigated as a function of temperature. Using the wafer curvature echnique, real-time strain relaxation curves are generated. These measurements how a sudden onset of relaxation of up to 22% of the epitaxial strain upon reaching emperatures in the range of 500 to 550C. The strong temperature dependence of his initial relaxation event is indicative of a BDT as predicted by the KPV model.