Zinc oxide films prepared by sol-gel spin-coating

The d.c. electrical conductivity and optical properties of undoped zinc oxi de films prepared by the sol-gel process using a spin-coating technique wer e investigated. The ZnO films were obtained by 10 cycle spin-coated and dri ed zinc acetate films followed by annealing in air at 500-575 degrees C. Th e films deposited on the Pyrex glass substrate were polycrystalline and c-a xis oriented. A minimum film resistivity gave 28.2 Omega cm at an annealing temperature of 525 degrees C. The temperature dependence of the conductivi ty indicated electron transport in the conduction band due to thermal excit ation of donor electrons for temperatures from 250 to 300 K. The grain boun dary scattering effect due to thermionic emission was confirmed. For temper atures below 250 K nearest-neighbor hopping conduction was dominant in the films. The films were transparent in the visible range above 400 nm and had sharp ultraviolet absorption edges at 380 nm. The absorption edge analysis revealed that the optical band gap energy for the films was 3.20-3.21 eV a nd the electronic transition was of the direct transition type. From the Ur bach tail analysis the width of the localized state E-e = 0.07-0.08 eV. (C) 2000 Elsevier Science S.A. All rights reserved.