Optical phonon localization in self-assembled Ge islands

We present a Raman scattering study for self-organized Ge islands on Si substrate carried out at 10 K. By means of difference Raman spectroscopy technique, we have separated the Raman signals from the Ge islands and Si substrate. The wetting layer thickness and strain were estimated from the line width and frequency peak. The estimated wetting layer thickness values are comparative with the Ge dot height obtained from microscopy measurements. The strain is decreased with an increase of the thickness.