Vibrational modes in ZnGeN2: Raman study and theory

Timothy J. Peshek, Tula R. Paudel, Kathleen Kash, and Walter R. L. Lambrecht
Phys. Rev. B 77, 235213 – Published 23 June 2008

Abstract

Polarized Raman spectra were measured for single crystals and polycrystalline ZnGeN2 grown by a vapor-liquid-solid method. A group-theoretical analysis of the selection rules governing the predicted dependence of the spectra on incoming and outgoing wave polarizations and propagation direction is presented. First-order Raman spectra corresponding to the zone center phonons are calculated from first principles using density functional perturbation theory. The Brillouin zone integrated density of phonon states is also calculated. Comparison of theory and experiment allows us to identify the a1t symmetry modes. However, vibrational density of states features deviating from the pure a1t spectrum are also visible in the experimental spectra and indicate some relaxation of momentum conservation rules. Differences in the experimental spectra under different polarization conditions are compared to the calculations. These differences allow us to identify different a1t Raman tensor components as well as to obtain at least partial information on the b2t modes. The much weaker polarization dependence in experiment than in theory, however, can at least in part be explained by using wurtzite-type selection rules. The observation of features explainable with wurtzite together with orthorhombic selection rules suggest that there is only partial ordering of the cations on their sublattice.

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  • Received 3 March 2008

DOI:https://doi.org/10.1103/PhysRevB.77.235213

©2008 American Physical Society

Authors & Affiliations

Timothy J. Peshek, Tula R. Paudel, Kathleen Kash, and Walter R. L. Lambrecht

  • Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079, USA

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Issue

Vol. 77, Iss. 23 — 15 June 2008

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