Fabrication and characteristics of transparent conducting In2O3–ZnO thin films by ultrasonic spray pyrolysis

Transparent conducting In2O3–ZnO thin films were prepared by ultrasonic spray pyrolysis technique. Indium nitrate trihydrate (In(NO3)3·3H2O) and zinc acetate dihydrate (Zn(CH3COO)2·2H2O) were used as precursors and a solvent was 2-methoxyethanol. The thin films, as a function of Zn/(Zn + In) atomic ratio (abbreviated to x), were annealed at 550 °C. Oxygen gas was used as both carrier and reactor gas. From analyzing X-ray diffraction patterns, In2O3 phase and ZnO phase were formed at x = 0.11 and 0.89, respectively, while homologous phases of In2O3–ZnO were observed between x = 0.5 and 0.67. The resistivity of the thin film increased until x = 0.33 and then decreased to be the lowest value (1.47 × 10−2 Ω cm) at x = 0.5. In the range of x = 0.6–1, the resistivity increased again with x. The highest carrier concentration and the highest Hall mobility were 2.02 × 1019 cm−3 at x = 0.6 and 15.89 cm2/V s at x = 0.5, respectively. The optical transmittance in the visible region at x = 0.5 was 88–92%.