We report highhyphen;resolution xhyphen;ray diffraction measurements of relaxed Si0.7Ge0.3layers on (001) Si substrates. Strain was relieved either by a glidehyphen;limited mechanism in structures where the composition was changed abruptly or by a nucleationhyphen;limited mechanism in structures having a compositionally graded intermediate layer. We find that the broadening of the xhyphen;ray peak of the surface alloy layer is similar in both cases, although the threading dislocation densities ranged from 1011cmminus;2to 5times;106cmminus;2. The effect of the threading dislocations on the xhyphen;ray peak widths is masked by the mosaic structure caused by the network of misfit dislocations underneath the layer.
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