Raman Efficiency in SiGe Alloys

Raman spectroscopy is commonly used for the optical characterization of structural properties of SiGe alloys, but a measurement of the Raman efficiency as a function of excitation wavelength and concentration is still lacking. This information is nevertheless important for the interpretation of data, especially for the analysis of inhomogeneous samples. In this work, the relative Raman efficiency of Si1−xGex alloys has been obtained for several excitation energies as a function of the composition x with steps of x = 0.02 across the whole composition range. We observed resonances in correspondence of the E1 / E1+1 and E0 / E0+0 transitions. For a fixed excitation energy the efficiency varies of about two orders of magnitude vs. the composition of the alloy, while, for a fixed composition, we observed a change in efficiency of up to three orders of magnitude depending on the excitation energy. The maximum scattering efficiency at resonance decreases by an order of magnitude when moving from silicon-rich to germanium-rich alloys. The data are discussed in terms of the polarizability and compared to the literature relative to pure silicon and germanium. The data reported in this paper can be used to design experiments under resonant conditions to selectively probe different regions in inhomogeneous samples.