Temperature dependence of raman scattering in ZnO

We present a Raman scattering study of wurtzite ZnO over a temperature range from 80 to 750 K. Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations. The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously. Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes. High-resolution spectra of the E-2(high), A(1)(LO), and E-1(LO) modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out. The E-2(high) mode displays a visibly asymmetric line shape. This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the K point, where the two-phonon density of states displays a sharp edge around the E-2(high) frequency. The temperature dependence of the linewidth and frequency of the E-2(high) mode is well described by a perturbation-theory renormalization of the harmonic E-2(high) frequency resulting from the interaction with the acoustic two-phonon density of states. In contrast, the A(1)(LO) and E-1(LO) frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel.