Pressure dependence of the optical and vibrational properties of hexagonal and cubic CdS films grown on GaAs

Abstract

The pressure dependence of the excitonic photoluminescence and Raman scattering in both hexagonal and cubic CdS films grown on GaAs substrates is reported. We found that the pressure coefficients of the cubic CdS films are equal to those of the hexagonal films within experimental uncertainties. The main difference between their optical and vibrational properties seems to lie in their exciton energies, the hexagonal phase having a slightly higher energy than the cubic phase. Strong enhancement in multi-longitudinal optical (LO) phonon scattering has been observed by "pressure-tuning" the exciton energy to resonate with the excitation laser line. As a result we have been able to determine the pressure coefficients of the higher order LO phonons in CdS for modes as high as 5LO. We found that the pressure coefficients of these higher order LO modes when normalized by the phonon frequency exhibit a systematic decrease with the order of the mode.

Off‐resonance Raman analysis of wurtzite CdS ground to the nanoscale: structural and size‐related effects

“…S1(a): supporting information) only shows the d = 0.2069-nm peak of the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) plane of greenockite (h-CdS mineral; JCPDS 41-1049). The diagrams recorded on fragments of gently crushed platelets ( Fig.…”

“…S1(b): supporting information) confirm that the crystal mainly consists of h-CdS but discontinuous diffraction rings also reveal a dispersion of cubic moieties. The crystal is oriented with c-hexagonal axis in the platelet surface and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) axis perpendicular to that surface ( Fig. 1).…”

Wave vector dependence of the pressure coefficient of the longitudinal optical phonon in CdS

“…This method can be applied to many ionic and partially ionic crystals which exhibit strong multi-LO phonon modes due to resonance with excitons. As an example, we extracted the wave vector dependence of γ(ω, q) of the LO phonon in CdS from recent experimental results [3].…”

“…The present work is motivated by our measurement of the pressure (P) dependence of multilongitudinal optical (nLO) phonon Raman modes in CdS films grown on GaAs substrates under resonance conditions [3]. As a result of resonance of the scattered photon energies with the lowest energy A…”

“…This method can be applied to many ionic and partially ionic crystals which exhibit strong multi-LO phonon modes due to resonance with excitons. As an example, we extracted the wave vector dependence of γ(ω, q) of the LO phonon in CdS from recent experimental results [3].The present work is motivated by our measurement of the pressure (P) dependence of multilongitudinal optical (nLO) phonon Raman modes in CdS films grown on GaAs substrates under resonance conditions [3]. As a result of resonance of the scattered photon energies with the lowest energy A…”