Pressure‐Raman study of resonant TO(Γ)–two‐phonon decay processes in ZnS: Comparison of three isotope compositions

Abstract

Pressure-Raman studies (to 15 GPa, at 300 K and 16 K) are reported on 64 Zn 34 S, 68Zn 32 S, and natural ZnS to compare the effects of resonant 3-phonon mixing on the TO(Γ) phonons for the different isotope compositions. Under pressure the TO(Γ) Raman profiles exhibit several distinct features, and a sharp Lorentzian TO(Γ) peak eventually emerges at a threshold pressure P Th that differs for each isotope composition. These effects are due to resonant mixing of the TO(Γ) phonon with TA + LA combination modes. Calculations based on a bond-charge model and perturbation theory reproduce the observed pressure variations in the shape and the width of the TO(Γ) peaks. It is shown that these changes relate to singularities in the TA + LA density of states. Mass scaling of the TO(Γ) and TA + LA modes explains the isotope effect on P Th , and leads to the estimate γ LA(W) ∼1.2.

Chemical vapor transport of zinc sulfide

“…The growth parameters are listed in Table 1. The grown cubic crystals have been used to study the mass and pressure dependence of phonon frequencies and line widths by Raman spectroscopy [9][10][11], to investigate the mass dependence of exciton energies by photoluminescence [12], and also to measure the specific heat in comparison with theoretical calculations [13].…”

“…In the present work, crystals of ZnS were grown for fundamental research. Especially, the mass and pressure dependencies of phonon frequencies and line widths of Raman spectra, anharmonicity effects in the lattice dynamics [9][10][11], the effect of isotopic mass variation on the photoluminescence spectra and the band gap, and on the electronic, vibrational, and thermodynamic properties have been studied on isotope substituted crystals [12,13].…”

Phonons of hexagonal BN under pressure: Effects of isotopic composition

“…Raman scattering experiments on isotopically enriched crystals under pressure can yield detailed information about the interplay between mechanisms determining phonon lifetime such as anharmonicity and isotopic disorder. Indeed, large variations of phonon lifetimes as a function of pressure and isotopic composition were reported in zinc-blende and wurtzite semiconductors, namely, CuI [28], ZnS [29], and ZnO [30]. Similar studies on layered materials are lacking in the literature.…”