Effect of phonon anharmonicity on thermal conductivity of ZnTe Thin films

Abstract

The ZnTe thin film is a potential material for optoelectronic devices in extreme temperature and radiation environments. In this report, the thermal conductivity of ZnTe films is measured non-invasively using the micro-Raman method and correlated with the phonon anharmonic effect. The evolution of crystalline ZnTe thin films from Te/ZnO bilayer by thermal annealing at 450 ∘C has been observed above the melting point of Te, which is confirmed from x-ray diffraction and high-resolution transmission electron microscopy. The ZnTe thin films illustrate three longitudinal phonon modes with higher harmonics of nLO (n = 3) at room temperature. Temperature-dependent Raman spectra in the range of 93–303 K are used to analyze the phonon anharmonicity from Raman shift, FWHM, and Phonon lifetime of the thin films. The Balkanski model is used to fit the anharmonicity-induced phonon frequency shift of nLO modes as a function of temperature, taking into account three- and four-phonon interactions. The intensity ratio of the I 2LO /I 1LO and I 3LO /I 2LO provide information about the electron-phonon coupling strength, which is influenced by the anharmonic effect. The laser power-dependent Raman spectra are used to determine the thermal conductivity of the ZnTe films, which is found to be approximately 9.68 Wm−1K−1, remains relatively constant for all nLO modes, indicating that multi-phonon scattering process. The correlation between thermal conductivity and phonon anharmonicity can pave the way for understanding the phonon scattering process in ZnTe thin films for high-performance optoelectronic device applications in harsh conditions.