In order to realize high thermoelectric performance of thin films, it was tried to control both high electrical conductivity (σ) and low thermal conductivity (K) for the 800 ppm Sn-doped indium-zinc oxide (IZO:Sn) films prepared by DC magnetron sputtering. The as-deposited films at RT and post-annealed films at 100-500°C showed amorphous structure, while the film annealed at 600°C was crystallized. The highest Power Factor was obtained for the film post-annealed at 200°C, which was due to the highest σ. However, the highest ZT was obtained for the films annealed at 500°C, which is mainly contributed to the lowest K and high σ. This result could be attributed to both amorphous structure with low thermal conductivity by phonon and the highest Hall mobility (low carrier density). Carrier density(n) and Hall mobility(μ) of the film could be controlled by both heat treatment and Sn doping with high bond enthalpy. Hence, these films can be considered as promising thermoelectric materials for applications in thermoelectric micro devices.
Secondly, we investigated thermoelectric properties of amorphous IZO and crystalline IZO. ITO and IZO films were crystallized at RT and 200 ˚C, respectively. In case of ITO, the lowest resistivity(ρ) of the film was observed at deposition temperature(Ts)=200˚C due to high μ. In case of IZO, the lowest ρ of the film was observed at RT indicating that ρ was increased with increasing deposition temperature, which is due to decrease in carrier density. This result could be attributed to increase of Zn2+ ions substituted In3+ site at high Ts. The highest Seebeck coefficient(S) were observed for ITO film deposited at RT and IZO film deposited at 200˚C respectively. The lowest of the carrier density led to the highest Seebeck coefficient. As a result, the highest power factor was estimated for the ITO film deposited at 200℃ and IZO film deposited at RT respectively. Because power factor was more dominated by electrical conductivity compare to Seebeck coefficient in relation to the carrier concentration. Furthermore, it is expected that the IZO film has the highest ZT. Because amorphous structure has low K, compared to high crystallinity, which is due to low K by the phonon. In this study, we can successfully prepared amorphous IZO film with good thermoelectric performance, which has high σ due to both high μ and low n.