N. Zotov et al., Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution, J PHYS-COND, 11(48), 1999, pp. 9647-9658
The Raman spectra of nine 216-atom models of amorphous silicon (a-Si) are c
alculated using the bond polarizability approximation of Raman scattering.
These a-Si models, generated by the activation relaxation technique, have d
ifferent concentrations of coordination defects, ring statistics and local
strain distributions, which cause changes in the vibrational density of sta
tes and the Raman scattering. Analysis of the vibrational modes indicates t
hat an increase in the number of coordination defects leads to an increase
in the high-frequency localization and to mixing of the TA modes with other
high-frequency modes. Calculation of partial Raman spectra indicates that
five-coordinated Si atoms enhance the high-frequency part of the LO Raman p
eak at about 400 cm(-1) and lead to characteristic band at about 600 cm(-1)
on the high-frequency side of the TO Raman peak. For their part, the three
-coordinated Si atoms contribute to the low-frequency part of the LO peak.
A weak correlation between the number of four-membered rings and the intens
ity of the LO Raman peak is also established although there is no correlati
on between the number of three- and four-membered rings and the total strai
n energy.