Thermal transport properties of polycrystalline tin-doped indium oxide films

Thermal diffusivity of polycrystalline tin-doped indium oxide (ITO) films with a thickness of 200 nm has been characterized quantitatively by subnanosecond laser pulse irradiation and thermoreflectance measurement. ITO films sandwiched by molybdenum (Mo) films were prepared on a fused silica substrate by dc magnetron sputtering using an oxide ceramic ITO target (90 wt % In2O3 and 10 wt % SnO2). The resistivity and carrier density of the ITO films ranged from 2.9×10−4 to 3.2×10−3 Ω cm and from 1.9×1020 to 1.2×1021 cm−3, respectively. The thermal diffusivity of the ITO films was (1.5–2.2)×10−6 m2/s, depending on the electrical conductivity. The thermal conductivity carried by free electrons was estimated using the Wiedemann–Franz law. The phonon contribution to the heat transfer in ITO films with various resistivities was found to be almost constant (λph=3.95 W/m K), which was about twice that for amorphous indium zinc oxide films.