Thermal conduction in polycrystalline or amorphous transparent conductive oxide films

With the widespread utilization of transparent conductive oxides (TCO) in various electronic devices, it is beneficial to revisit the fundamentals of heat conduction to formulate a comprehensive physical understanding for thermal properties of TCOs with the aim of improving the thermal design of electronic devices. For degenerate polycrystalline TCO films, both free electrons and phonons act as heat carriers, where free electron contribution can be calculated based on the Wiedemann-Franz law.Interestingly, the phonon thermal conductivity remains almost constant for degenerated polycrystalline TCO films with different dopant concentrations, suggesting the existence of dopant-induced minimum phonon thermal conductivity. For degenerate amorphous TCO film, free electrons act as heat carriers along the conduction path formed by the orbital overlap of cations, which also obey the Wiedemann-Franz law. Moreover, the atomic vibration contribution to thermal conductivity almost keeps unchanged for amorphous TCO films deposited under different conditions, indicating the existence of a minimum thermal conductivity caused by the scattering of vibrational mode due to structural randomness appeared in the bond angle. We anticipate that these fundamental understanding can provide a guide for the discovery of TCO materials with optimized thermal properties.