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 200 nm 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 (89.3 wt % In2O3 and 10.7. wt % ZnO). The resistivity, carrier density, and Hall mobility of the IZO films ranged from 4.2 X 10(-4) to 22.7 Omega cm, from 2.6 X 10(16) to 4.2 X 10(20) cm(-3), and from 10 to 51 cm(2)/V s, 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) X 10(-6) M-2/ 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 (lambda(ph)= 1.85 W/m K), which was about half of the one for polycrystalline indium tin oxide films.