Correlation between low frequency vibrational excitations and glass transition dynamics in amorphous semiconductors Ge1−xSx

The structural relaxation in the glass transition of amorphous semiconductors Ge1−xSx (0.63 ⩽ x ⩽ 0.90) has been investigated by differential scanning calorimetry. The heat capacity curves were analyzed by the Moynihan formulation with a Kohlrausch–Williams–Watts (stretched exponential) relaxation function and a Narayanaswamy relaxation time. A fractal dimension was derived from the nonexponentiality of the relaxation using a free-volume theory, and was found to decrease with the addition of S from about 2.1 for x = 0.63 to about 1.8 for x = 0.90. A thermokinetic dimension was also calculated from the activation energy of the relaxation using dimensionally-expanded Kissinger plots. We have found that the two dimensions are in good agreement with the fractal dimension obtained from the low frequency Raman scattering spectra. The observations suggest that the change in the fractal dimension is associated with the lowering of the network dimensionality due to the weakening of bond constraints with the addition of S.