Low-temperature deposition of transparent ZnO films by the ultrasonic-mediated stepwise method

A novel solution method was developed for the deposition of transparent ZnO film from aqueous solution, integrating the ultrasonic irradiation with the stepwise chemical deposition at relatively high temperature (>100 °C). Obtained ZnO films exhibited high crystallinity, highly preferential orientation along the c-axis, smooth and compact morphology, and high transmittance in the visible band (>80%). The deposition temperature and ultrasonic irradiation were found to have significant influence on the phase purity, crystallinity, grain size, and morphology of ZnO films. While the lower temperature (120 °C) was inefficient to eliminate the intermediate phase of Zn(OH)2, the higher deposition temperature and ultrasonic irradiation were found powerful to improve the crystalline degree and the quality of film. Mechanism analysis indicated that the rapid water evaporation in the precursor layer and the rapid decomposition of zinc–ammonia complex during the high-temperature deposition process were indispensable for the growth of high-quality ZnO films.