Multiphonon processes in ZnO

Abstract

Using space group theoretical method we have determined the Lattice Mode Representation (LMR) for ZnO with the space group C6v4 (P63mc). The reduction of the LMR onto irreducible species of the C6v4 space group leads to the total number of independent first order vibrational modes and their symmetries (irreducible representations of Gk/T) originating from the centre (k=0) as well as from the high symmetry points and lines (k=0) of the hexagonal Brillouin zone (BZ) for ZnO. Considering only long-wave-length modes (k ≅ 0) we have derived Raman selection rules for the first, second, and third order Raman active modes, hereafter referred to as 1RAMs, 2RAMs, and 3RAMs, respectively. We have also performed the back scattering Raman spectroscopy from ZnO in the frequency regions of the 1RAMs, 2RAMs, and 3RAMs. Several muliphonon processes have been observed. In addition, the low temperature photoluminescence (PL) spectra exhibit some phonon replicas confirming the presence of the multiphonon processes in ZnO. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.