Electrical and optical properties of In2O3-ZnO thin films prepared by sol-gel method

Transparent conducting indium zinc oxide (In2O3-ZnO) thin films were fabricated by a sol-gel method. Zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and indium nitrate trihydrate [In(NO3)3·3H2O] were used as starting precursors, and 2-methoxyethanol as a solvent. Monoethanolamine was added as a stabilizer. The starting solution was spin-coated onto a glass substrate. Thin films at several atomic ratios of Zn/(Zn + In) were annealed at 650 °C. The minimum resistivity (ρ ≈ 1.5 × 10− 3 Ω cm) and maximum carrier concentration (n ≈ 3.0 × 1020 cm− 3) were obtained for the film whose atomic ratio was 0.5. The optical transmittance in the visible region was 80−85% irrespective of atomic ratios. After the Zn2In2O5 (a homologous compound ZnkIn2Ok+3 where k = 2 and corresponds to the atomic ratio of 0.5) films were post-annealed in a reducing atmosphere, the carrier concentration increased to approximately 4.0 × 1020 cm− 3 and the optical window was narrower, although the resistivity slightly increased.