A mechanism for 'double half dislocation loops' nucleation in low misfit epitaxial Ge_x Si_(1-x) on Si

摘要

A three-stage mechanism is discussed for the formation of "double half loops" observed by Perovic and Houghton (1992) in low misift epitaxial layers of Ge_x Si_(1-x) on Si. First, prismatic loops are nucleated in Ge precipitates at the interface to relieve their strain. Second, these loops are transformed into two glide loops on different (111) planes. Third, these loops bow out by growth of the precipitates in the epitaxial layer and expand along the interface. On reaching a critical size, the loops expand in the epitaxial layer to form the "double half loops". Several steps in the process are controlled by vacancy concentration and diffusion and are consistent with the recently reported reduction in nucleation density by Si irradiation (Stirpe et al 1997).