Pressure-induced phonon freezing in the ZnSeS II–VI mixed crystal: phonon–polaritons andab initiocalculations

Abstract

Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the 'phonon-polariton' transverse optical modes (with mixed electrical-mechanical character) of the II-VI ZnSe1-x S x mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly-resolved percolation-type Zn-S Raman doublet of the three oscillator [1 × (Zn-Se), 2 × (Zn-S)] ZnSe0.68S0.32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende → rocksalt), as determined by high-pressure x-ray diffraction. We find that the intensity of the lower Zn-S sub-mode of ZnSe0.68S0.32, due to Zn-S bonds vibrating in their own (S-like) environment, decreases under pressure (Raman scattering), whereas its frequency progressively converges onto that of the upper Zn-S sub-mode, due to Zn-S vibrations in the foreign (Se-like) environment (ab initio calculations). Ultimately, only the latter sub-mode survives. A similar 'phonon freezing' was earlier evidenced with the well-resolved percolation-type Be-Se doublet of Zn1-x Be x Se (Pradhan et al 2010 Phys. Rev. B 81 115207), that exhibits a large contrast in the pressure-induced structural transitions of its end compounds. We deduce that the above collapse/convergence process is intrinsic to the percolation doublet of a short bond under pressure, at least in a ZnSe-based mixed crystal, and not due to any pressure-induced structural transition.

Effect of sulfur on the scintillation properties of mixed ZnSxSe1–x crystals

“…Смåшàííым êðèñòàëëàм ZnS x Se 1-x ïîñâÿщå-íî мíîãî ïóбëèêàцèé, íî â бîëьшèíñòâå èз íèõ îïèñàíы êðèñòàëëы, âыðàщåííыå èз ïàðîâîé фàзы, è ëèшь â íåмíîãèõ -êðèñòàëëы, ïî-ëóчåííыå мåòîдîм âыðàщèâàíèÿ èз ðàñïëàâà [7][8][9][10][11]. Одíàêî èмåííî мåòîды íàïðàâëåííîé êðèñòàëëèзàцèè ïîзâîëÿюò ñîздàâàòь êðèñòàëëы ZnS x Se 1-x дîñòàòîчíî бîëьшèõ ðàзмåðîâ, ïðèãîд-íыå, êàê óжå îòмåчàëîñь, дëÿ ñîздàíèÿ дåòåê-òîðîâ чàñòèц âыñîêîé ýíåðãèè.…”

The growth, structure and luminescence properties of ZnSe1-xSx materials

“…The position of the energy levels of radiative recombination centres in the band gap of ZnSe 1-x S x crystals can be easily changed [18,19]. There are different methods to obtain ZnSe 1-x S x mixed crystals, most of them using vapour phase growth methods [20] and only a few concern the directional solidification techniques which allow obtaining large ZnSe 1-x S x mixed crystals [21][22][23].…”

Band Gap Change of Bulk ZnSxSe1–x Semiconductors by Controlling the Sulfur Content

“…But these techniques do not allow one to fabricate large ZnS Se 1− crystals required for x-ray and -ray detectors. Large ZnS Se 1− crystals can be grown by the directional solidification techniques [10][11][12][13][14]. Up to now, few publications were devoted to the growth of ZnS Se 1− bulk crystals [10][11][12][13][14] and growing a massive ZnS Se 1− crystal with required properties is still a challenge.…”

“…Large ZnS Se 1− crystals can be grown by the directional solidification techniques [10][11][12][13][14]. Up to now, few publications were devoted to the growth of ZnS Se 1− bulk crystals [10][11][12][13][14] and growing a massive ZnS Se 1− crystal with required properties is still a challenge. A variation of the sulfur content in ZnS Se 1− bulk crystals changes the growth conditions and can lead to the appearance of different defects or can change the type of chemical bonds, which, in turn, influences the width of the optical band gap [15,16].…”