TWINNING AND THE FORMATION OF THE DIAMOND HEXAGONAL PHASE IN SI-GE SHORT-PERIOD SUPERLATTICES

The structure of as-grown and thermally annealed (Si17.5Ge7)8 atomic layer superlattices has been studied by cross-sectional and plan view transmission electron microscopy. The as-grown structure contains twins and small clusters identified as the diamond hexagonal phase. The volume fraction of twins and the diamond hexagonal phase increase on annealing at 700-degrees-C as the stresses in the structure are relaxed. The formation of the diamond hexagonal phase is thought to occur at twin-twin intersections, as previously reported in the literature for Si and Ge subjected to high stresses during indentation testing.