Raman spectra of ͑AlN͒ 8Ϫ␦ /(Al x Ga 1Ϫx N) ␦ /͑GaN͒ 8Ϫ␦ /(Al x Ga 1Ϫx N) ␦ superlattices with interface thickness varying between ␦ϭ0 and ␦ϭ3 are calculated. The influence of the nonabrupt interface related broadening is described in the complete range of scattering, with special attention to the modes giving stronger contribution to the Raman intensity. It is shown that the dispersion of folded acoustic phonons does not change appreciably with the interface smoothing. For ␦ϭ0 the Raman spectra display new peaks due to the enhancement of some confined optic modes.

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Raman spectra of (3C–SiC)8−δ/(3C–SiC0.5Si0.5)δ/(Si)8−δ/(3C–SiC0.5Si0.5)δ superlattices with interfacial transition regions of thickness δ varying from one to three monolayers are calculated. It is shown that severe frequency shifts (up to −86 cm−1) and the flattening of the folded optical phonons dispersion curves are due to the interfacial regions, strongly affecting the Raman spectrum in consequence. With increasing interface thickness, the Raman peaks are enhanced in the middle frequency range. These effects are mainly attributed to localization of atomic displacements at the Si/3C–SiC or the 3C–SiC/Si interfacial transition regions.