Interface mode in Si/Ge superlattices: Theory and experiments

The Raman peak associated with Si-Ge vibrations in short-period Si/Ge (001) superlattices is studied both experimentally and theoretically. On the experimental side, we use a microprobe technique which allows us to investigate the longitudinal (L) and transverse (T) spectra, and find an unexpected behavior of the line shape and L-T spitting of this peak. By means of first-principles calculations, taking into account both strain and interface intermixing, we show that such behavior is consistent with the picture of an intermixed alloy layer at the interfaces, and we are able to identify the character and spatial localization of the individual atomic clusters contributing to the vibrations.