Influence of annealing temperature on structural and optical properties of ZnO: In thin films prepared by ultrasonic spray technique

Transparent conducting indium doped zinc oxide was deposited on glass substrate by ultrasonic spray method. The In doped ZnO samples with indium concentration of 3 wt.% were deposited at 300, 350 and 400 degrees C with 2 min of deposition time. The effects of substrate temperature and annealing temperature on the structural, electrical and optical properties were examined. The DRX analyses indicated that In doped ZnO films have polycrystalline nature and hexagonal wurtzite structure with (002) preferential orientation and the maximum average crystallite size of ZnO: In before and annealed at 500 degrees C were 45.78 and 55.47 nm at a substrate temperature of 350 degrees C. The crystallinity of the thin films increased by increasing the substrate temperature up 350 degrees C, the crystallinity improved after annealing temperature at 500 degrees C. The film annealed at 500 degrees C and deposited at 350 degrees C show lower absorption within the visible wavelength region. The band gap energy increased from E-g = 3.25 to 3.36 eV for without annealing and annealed films at 500 degrees C, respectively, indicating that the increase in the transition tail width. This is due to the increase in the electrical conductivity of the films after annealing temperature. (C) 2012 Elsevier Ltd. All rights reserved.