Heterogeneous nucleation sources in molecular beam epitaxy-grown Ge xSi 1− x/Si strained layer superlattices

Abstract

In the past few years, a number of studies have indicated the importance of heterogeneous sources in understanding defect nucleation mechanisms. Nonetheless, the majority of critical thickness research is still based on homogeneous misfit dislocation nucleation theory to predict the onset of plastic relaxation at strained layer interfaces. It will be shown that heterogeneous sources are plentiful even in molecular beam epitaxy (MBE)-grown material wherein the generation of defects depends on the oxygen/carbon contamination levels. Several metastable Ge x Si 1− x /Si strained layer superlattices have been grown under slightly different conditions in order to vary the concentration of oxygen/carbon at the substrate-buffer interface. Subsequent annealing treatments were carried out in order to accentuate any characteristic differences in the plastic relaxation behaviour of these metastable structures. Chemical defect etching, plan-view and cross-sectional transmission electron microscopy have been used extensively to characterize misfit dislocation nucleation behaviour at the strained layer interfaces based on differences in the number and type of heterogeneous sources.