PHOTOSENSITIVE ZNO THIN-FILMS PREPARED BY THE CHEMICAL-DEPOSITION METHOD SILAR

Structural, optical and photoresponse characteristics of ZnO thin films (similar to 0.1 mu m) prepared by a relatively new chemical deposition method, SILAR (successive ion layer adsorption and reaction), are described. The films are deposited by successive immersion of glass substrate in a dilute solution of Zn2+-ammonia complex at room temperature and in hot water (96 degrees C) for up to 35 immersion cycles using a computerized electropneumatic deposition system. Film thickness varied from 0.02 mu m (6 cycles) to 0.11 mu m (35 cycles). The as-prepared films show hexagonal (zincite) structure with a preferred orientation-c-axis perpendicular to the plane of glass substrate-but lose this preferential orientation when annealed at 350 degrees C. An optical transmittance of 90% combined with a specular reflectance of 10% in the visible and near-infrared region is typical of these films. The as-prepared films show a photocurrent to dark current ratio of 10(5) under 900 W m(-2) illumination from a solar simulator. The dark conductivity and photoconductivity are influenced by heat treatments in controlled atmospheres (O-2, H-2 and air).