An annealing study of relaxation and interface quality in Si-Si1−xGex strained-layer superlattices

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Abstract
The relaxation and interface quality of two representative molecular‐beam‐epitaxy‐grown Si‐Si1−xGex strained‐layer superlattices have been investigated by Raman scattering spectroscopy, double‐crystal x‐ray diffraction, transmission electron microscopy, and charge collection microscopy in a scanning electron microscope. One of the superlattices appeared stable, and the other metastable, under thermal annealing at temperatures between 600 and 900 °C. The strain values perpendicular to the growth direction as a function of annealing temperature are obtained from a kinematical simulation of x‐ray rocking curves. These results are compared with the frequency shifts of the longitudinal optical phonons in the Raman spectra. Deterioration of the crystal quality and progressive relaxation was observed in the metastable superlattice. The thermally induced relaxation occurred through formation of misfit dislocations at the first Si‐Si1−xGex interface and these caused threading dislocations to form within the epilayer. The degradation of the interfaces for both superlattices on annealing is correlated with a sharp decrease in the acoustic mode Raman intensities.