Study on the growth and optical properties of ZnO thin films fabricated by ultrasonic spray pyrolysis

In this paper, ZnO nanofilms are prepared on quartz substrate by ultrasonic spray pyrolysis (USP) technology. The effects of substrate temperature and deposition time on the micro-structural, morphological and optical properties of ZnO thin films are investigated in detail. Measurements indicate that the growth process of the film is as follows: Micro grains accumulation -> grains' expansion -> grow into certain nanostructures under different temperature. Nanostructures of the film are as follows: Irregular broken hexagonal-like structure (< 450 degrees C); coexisting of broken hexagonal- and sheet-like structure (450-500 degrees C); regular closed packed sheets-like structure (> 500 degrees C). In addition, all results show that RMS roughness of the films is less than 20 nm. Moreover, the visible transmittance of these samples is higher than 90%. Which display that ZnO films with low roughness and excellent optical properties can be also fabricated by low-cost USP method.