A series of Si/Si,-,Ge, strained-layer superlattice structures has been studied by x-ray double-crystal diffractometry, Raman spectroscopy and transmission electron microscopy. The periodicity of the superlattices, the alloy composition and the degree of relaxation have been measured. The precisions of the three techniques are discussed and the results critically compared.
The density of misfit dislocation sources in strained Si1−xGex layers grown on Si substrates is rarely sufficient to explain the observed extent of relaxation when layer thicknesses are in excess of the metastable critical thickness. This letter describes a process whereby a small, but finite number of misfit dislocation nucleation sources can lead to extensive strain relaxation across a complete wafer. Two novel mechanisms for misfit dislocation multiplication are presented and shown to be compatible with microscopic observations of chemically etched layers.
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