Raman scattering in Ge1−ySny alloys

The Raman spectrum of nearly relaxed Ge1−ySny alloys grown on Si substrates was investigated for Sn concentrations y<0.2y<0.2. The frequency dependence of the Ge–Ge Raman mode was re-evaluated by carrying out careful corrections for residual strain shifts. The Ge–Sn mode was observed for the first time in this type of samples. Its frequency appears to decrease monotonically as a function of the Sn concentration. This is very different from the behavior of the Si–Ge mode in Si1−yGey alloys, but a detailed analysis suggest that there is a scaling relationship between these modes that is the analog of the scaling relationship found earlier for the Ge–Ge mode. Raman activity is also found in the spectral range where Sn–Sn modes are expected, but the polarization properties of these features suggest an overlap with disorder-activated Ge-acoustic phonons. Additional features observed in “forbidden” scattering configurations are also assigned to disorder-activated Raman scattering.