MODEL INVESTIGATION OF THE RAMAN-SPECTRA OF AMORPHOUS-SILICON

A model for calculating the first-order Raman spectra of amorphous sil icon (a-Si) without adjustable parameters is proposed. Calculations on the original 216-atom model of a-Si, generated by the algorithm of Wo oten, Winer, and Weaire (WWW) are in very good agreement with experime ntal spectra and give further indication that the WWW cluster is a rea listic model of moderately disordered a-Si. The TA-TO assignment of th e low and high frequency bands is supported by direct numerical calcul ations of the phase quotient and the stretching character of the vibra tional modes. The calculated participation ratios and correlation leng ths of the vibrational modes indicate that the high-frequency TO-like modes are strongly localized on defects. The relative intensities of t he TA-, LA-, and LO-like bands depend on the intermediate-range order, while that of the TO-like band mainly on the short-range order.