Phonon Densities of States and Eigenvectors in Hydrogenated and Fluorinated Amorphous Silicon

A study of the vibrational properties of amorphous silicon alloys is presented. Using the Cluster-Bethe-lattice method and isolated cluster calculations, local densities of states spectra and eigenvectors are calculated. Our results indicate that all of the vibrational modes associated with H and F in the alloys exhibit a localized character : those above 500 cm-1 are localized predominantly on the H or F sites, while those below are in-band resonances and localized within the first three layers of Si-atoms.