Germanium content and strain in Si1−xGex alloys characterized by Raman spectroscopy

Abstract

Previous Raman spectroscopy studies on SiGe alloys have left rather large uncertainties concerning the relationships between the Raman peaks׳ frequency shifts and stress. In this paper, we systematically revisit these relationships, confirm some coefficient values and propose new relationships linking the Raman peak shift to stress and Ge concentration. Different types of stacks were grown and studied to that end:(1) Thick, nearly fully relaxed SiGe virtual substrates grown on Si (001), whose lattice parameter is close to that of bulk material for a given Ge composition (in-between 20% and 100%).(2) Thin, fully compressively-strained SiGe layers grown on Si (001), with a Ge content in the 5–55% range.The cross-examination with Raman spectroscopy and X-ray diffraction of those stacks provided us with precise values of the coefficients linking the Raman peak shift to (i) the Ge content of the SiGe layer (thanks to SiGe virtual substrates) and (ii) the magnitude of stress in the SiGe layer (thanks to thin, fully pseudomorphic layers).