Effect of electrical properties on thermal diffusivity of amorphous indium zinc oxide films

Thermal diffusivity of amorphous transparent conductive films, indium zinc oxide (IZO) films, with a thickness of $200nm$ has been analyzed quantitatively using a newly developed nanosecond thermoreflectance system. IZO films sandwiched by molybdenum (Mo) films were prepared on fused silica substrate by dc magnetron sputtering using an oxide ceramic IZO target (⁠$89.3wt%$ $In2O3$ and $10.7wt%$ ZnO). The resistivity, carrier density, and Hall mobility of the IZO films ranged from $4.2×10−4to22.7Ωcm$⁠, from $2.6×1016to4.2×1020cm−3$⁠, and from $10to51cm2∕Vs$⁠, respectively. The thermoreflectance signals were analyzed based on an analytical solution of the one dimensional heat flow across the three-layered film (Mo/IZO/Mo) system. The thermal diffusivity of the IZO films was $(0.6–1.3)×10−6m2∕s$⁠, depending on the electrical resistivity. The thermal conductivity carried by free electrons was estimated using the Wiedemann-Franz law. The phonon contribution to the heat transfer in IZO films with various resistivities was found to be almost constant $(λph=1.85W∕mK)$⁠, which was about half of the one for polycrystalline indium tin oxide films.