LOW-FREQUENCY RAMAN-SCATTERING IN AMORPHOUS GEXS1-X

The low frequency Raman scattering of amorphous GexS1-x (0.07 less tha n or equal to X less than or equal to 0.37) was measured at 20 K. Two distinct vibration regimes were observed in the reduced Raman scatteri ng spectra after the subtraction of excess scattering. The regime at l ower frequency region where the reduced Raman intensity, I-R, is propo rtional to omega(4) is assumed to be due to the Debye-like acoustic ph onon. In the higher frequency region, the power-law index on the frequ ency is about 2.2 for X = 0.07, and decreases with the addition of Ge, and becomes 1.4 for X = 0.37. This regime was interpreted by a fracto n model. The experimental results suggest that the fractal dimension i ncreases with the addition of Ge. It is also found that the crossover frequency from Debye-like acoustic phonon to fracton decreases with th e decrease of X. The composition dependence of fractal dimension and t he density correlation length (3.3 nm for GeS2) are discussed. (C) 199 8 Elsevier Science B.V. All rights reserved.