Raman spectra of ultrathin Ge layers on Si substrates

Abstract

Strain in ultrathin Ge layers on (100) Si is measured by a Raman technique and compared with results of reflection high-energy electron diffraction (RHEED). When the Ge thickness is 7 mono-atomic layers (ML) and 10 ML, Raman results show that the layer is almost coherent to the Si lattice. In contrast, significant relaxation is observed for the same thicknesses by RHEED. For thicknesses larger than 10ML, both the measurements give an identical result that most of the mismatch strain is relaxed. This indicates that the relaxation due to dislocations begins at an average thickness of about 10ML.