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Abstract

The first- and second-order Raman spectra of cubic ZnS (beta-ZnS,
zinc-blende) are revisited. We consider spectra measured with two laser
lines for samples with different isotopic compositions, aiming at a
definitive assignment of the observed Raman features and the mechanisms
which determine the linewidth of the first order TO and LO Raman
phonons. For this purpose, the dependence of the observed spectra on
temperature and pressure is investigated. The linewidth of the TO
phonons is found to vary strongly with pressure and isotopic masses.
Pressure runs, up to 15 GPa, were performed at 16 K and 300 K. Whereas
well-defined TO Raman phonons were observed at low temperature in the
whole pressure range, at 300 K the TO phonons appear to hybridize
strongly with the two-phonon background and lose their identity,
especially in the (3-10)-GPa region. The intensity of the TO phonons,
which nearly vanishes when measured with a red laser line, is shown to
result from a destructive interference of the amplitudes of the
band-edge resonance and that of a background of opposite sign. The
analysis of these effects is aided by calculations of the densities of
one- and two-phonon states performed with the adiabatic bond charge
model of the lattice dynamics.