Structural and phonon properties of CdTe thin films synthesized by discrete thermal evaporation

Abstract

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 temperaturedependent 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 highefficiency 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.