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 u s 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 c onsistent with the picture of an intermixed alloy layer at the interfa ces, and we are able to identify the character and spatial localizatio n of the individual atomic clusters contributing to the vibrations.