The second-order Raman spectra of diamond and silicon have been calculated using ab initio phonons and phenomenological polarizability coefficients. The sharp peak in the spectrum of diamond near the two-phonon cutoff is explained by a maximum in the vibrational density of states; this maximum originates from the uppermost phonon branch whose frequencies are calculated to have a minimum at the Brillouin-zone center. This frequency minimum as well as the sharp Raman peak are unique to diamond and do not occur for the other group-IV semiconductors. In our calculation based on harmonic ab initio lattice dynamics neither two-phonon bound states nor polarizability matrix element effects are needed to explain the peak, and we feel that the longstanding controversy about its origin has been resolved.
2ND-ORDER RAMAN-SPECTRA OF DIAMOND FROM AB-INITIO PHONON CALCULATIONS
GIANNOZZI, Paolo;
1993-01-01
Abstract
The second-order Raman spectra of diamond and silicon have been calculated using ab initio phonons and phenomenological polarizability coefficients. The sharp peak in the spectrum of diamond near the two-phonon cutoff is explained by a maximum in the vibrational density of states; this maximum originates from the uppermost phonon branch whose frequencies are calculated to have a minimum at the Brillouin-zone center. This frequency minimum as well as the sharp Raman peak are unique to diamond and do not occur for the other group-IV semiconductors. In our calculation based on harmonic ab initio lattice dynamics neither two-phonon bound states nor polarizability matrix element effects are needed to explain the peak, and we feel that the longstanding controversy about its origin has been resolved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
