Oxygen vibrational modes in ZnS1−xOx alloys

Abstract

ZnS1−xOx alloy films were studied via resonant Raman spectroscopy. Films with a low oxygen content exhibit ZnS longitudinal optical modes and additional modes attributed to O local vibrational modes (LVMs). The frequencies of these modes are explained by a simple mass-defect model. As the O content increases, pairs and larger clusters form, causing the O mode to transition from an LVM to a delocalized phonon. The composition dependence of the modes shows agreement with the modified random element isodisplacement model. Low-temperature measurements show that the O-related mode is composed of multiple features, attributed to zincblende and wurtzite structural regions.

High Order Oxygen Local Vibrational Modes in ZnS1−xOx

“…That is, the behavior of the LVM is nearly unencumbered by modifications due to next‐nearest neighbor O atoms. However, with increasing O content the ZnS 1−x O x alloy system is predicted by the modified random element isodisplacement model to exhibit “two mode” behavior, in agreement with experiment . That is, the peak position of the LVM will shift to higher energies with increasing O content, similar to findings in other alloy systems .…”

“…Thin film samples were grown using rf magnetron sputtering on Al 2 O 3 (0001) substrates. The details of the growth process and composition measurements have been reported elsewhere . The bulk crystal is (111) oriented zincblende ZnS from Fairfield Crystal.…”

“…Extensive examination of literature has revealed only one similar case in resonant scattering: that of CdS:Cl where the local mode and LO overtones were observed . In our previous work, we found that the composition dependence of the LO and LVM modes can be modeled using the modifed random element isodisplacement (MREI) model, but the origin of the LVM + n LO combinations was not explored beyond showing that they result from outgoing resonance. In addition the presence of the 2LVM + LO modes was not reported or explored.…”

“…All materials display n LO harmonic modes ( n = 1,2,3 …). For ZnS 1−x O x additional peaks appear near ≈412 cm −1 which are attributed to local vibrational modes (LVMs) caused by substitution of the O on the S site in the lattice . Because O is lighter than S, substitutional O impurities (O S ) have a local vibrational mode (LVM), an oscillation that is localized in frequency and real space .…”