Raman scattering properties of amorphous As and Sb

Raman scattering measurements on bulk amorphous As and thin-film sputter-deposited amorphous As and Sb indicate differences in the vibrational character of the systems. The polarization properties of amorphous As indicate quasimolecular character with differences between the bulk and sputtered material attributed to local variations in structure beyond nearest neighbors. The Raman spectra of sputtered amorphous Sb, in contrast, indicate nonmolecular character as in group-IV amorphous systems. A comparison of neutron-scattering measurements with the Raman spectra has been used to gain information about the frequency dependence of the Raman coupling parameter. The approximate form of the coupling parameter near the lowest peak in the density of phonon states, which is also found to hold for amorphous Se and Ge, is used to estimate the form of the density of states of amorphous Sb. The low-frequency phonon spectrum in amorphous Sb differs appreciably from the crystalline rhombohedral form reflecting changes in the second of higher neighbor distributions.