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

Abstract Transparent conducting indium zinc oxide (In 2 O 3 –ZnO) thin films were fabricated by a sol–gel method. Zinc acetate dihydrate [Zn(CH 3 COO) 2 ·2H 2 O] and indium nitrate trihydrate [In(NO 3 ) 3 ·3H 2 O] 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 × 10 20 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 Zn 2 In 2 O 5 (a homologous compound Zn k In 2 O k +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 × 10 20 cm − 3 and the optical window was narrower, although the resistivity slightly increased.