Raman coupling-parameter variation in amorphous germanium

Inelastic neutron and Raman scattering measurements on amorphous Ge are combined to obtain the frequency variation of the depolarized and fully polarized Raman coupling parameters, $C^{\alpha }$(ω). These measurements were obtained on two forms of a-Ge chosen so as to maximize differences in the degrees of local short-range order. For both highly ordered and highly disordered forms of a-Ge the variation of $C^{\alpha }$(ω) is found to be qualitatively similar in overall form, although quantitative differences exist, particularly at low frequencies. The results provide a means of determining the phonon density of states of other forms of a-Ge thin films for which neutron measurements are not feasible. Qualitatively similar variations in $C^{\alpha }$(ω) for a-Si are also predicted.