Structural and phonon properties of CdTe thin films synthesized by discrete thermal evaporation
摘要
Despite the technological significance of CdTe, the influence of high-order phonon anharmonicity on phonon transport in thin films synthesized by discrete evaporation has not been sufficiently studied. This study investigates the temperature-dependent anharmonic phonon interactions in CdTe thin films synthesized by discrete thermal evaporation, to provide the basis of optimizing the thermo- and electrophysical properties of the material for use in high-performance photovoltaic and optoelectronic devices. The films, annealed in air at 400 °C, exhibited a cubic structure with near-stoichiometric composition (Cd/Te ≈ 1.1) and a grain size of ~ 1 µm. Temperature-dependent study analyzed the shifts and broadening of TO, LO, and 2LO phonon modes. Using the improved Klemens model, the contributions of thermal expansion as well as 3- and 4-phonon scattering were decoupled, revealing their distinct roles in phonon energy. Key findings include a nonlinear temperature dependence of phonon peak positions, with TO, LO, and 2LO modes shifting by 4.1, 5.6, and 10.7 cm−1, respectively, upon cooling to 40 K; dominance of 3-phonon scattering below 200 K, while 4-phonon interactions prevailed at higher temperatures, contributing to the shift up to 7.6 cm−1 for 2LO modes; and dominance of 3-phonon process contribution to phonon linewidth broadening below 105 K, whereupon the contribution of 4-phonon scattering became the main process responsible for the broadening. The demonstrated synthesis method yields films with structural and compositional suitability for high-efficiency solar cells, while the analysis of temperature-dependent Raman results highlights the critical role of high-order lattice anharmonicity in CdTe, providing a foundation for optimizing CdTe-based devices.