Investigation of Anisotropic Thermal Conductivity in Sb-Doped ZnO Thin Films Using Infrared Radiometry and Thermoreflectance Techniques along with First-Principles Calculation

Antimony (Sb) doped ZnO thin films are investigated to elucidate their anisotropic heat‑transport properties for advanced thermal management and thermoelectric applications. Films with Sb concentrations from 0 to 0.4 at.% were deposited by pulsed‑laser deposition onto sapphire substrates to ensure high crystalline quality, and characterized by X‑ray diffraction and atomic force microscopy to confirm phase purity, uniform dopant distribution, and surface morphology. We employ complementary infrared radiometry and frequency‑domain thermoreflectance to measure cross‑plane and in‑plane thermal conductivities at room temperature, with repeat measurements across a 300–500 K range to evaluate temperature dependence. Both conductivity components decrease monotonically with increasing Sb content reaching up to 40 % reduction at 0.4 at.% Sb consistent with enhanced phonon scattering induced by mass‑defect and strain‑field perturbations. All doped samples exhibit pronounced thermal anisotropy: in‑plane conductivities exceed cross‑plane values by 30–60 %, with measurement uncertainties below ±5 %. Complementary density functional theory calculations using Quantum ESPRESSO reveal that Sb‑induced lattice distortions and local strain fields modify phonon dispersion relations and increase scattering rates, corroborating experimental observations. Figure 1 illustrates the evolution of both conductivity components with doping concentration and underscores the persistent anisotropic behavior. These high‑precision, multi‑technique measurements deliver unprecedented insight into phonon‑mediated heat conduction in doped semiconducting oxides, establish critical benchmarks for the rational design of high‑performance thermal barrier coatings, and inform optimization strategies for next‑generation thermoelectric modules and integrated thermal management systems

Figure 1. Variation of in‑plane and cross‑plane thermal conductivities in Sb‑doped ZnO thin films with increasing Sb content (0–0.4 at. %), highlighting anisotropic heat transport.