Raman coupling-parameter variation in amorphous germanium

Abstract

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.