Microstructure and optical properties of AlOx thin films grown on ZnO-deposited glass

Abstract

AlOx thin films were grown on ZnO-deposited glass substrates under different conditions using magnetron sputtering. The influence of processing parameters (mainly direct-current power and oxidizing atmosphere) on the structure and optical properties were investigated. The AlOx films for all samples in this study showed the coexistence of amorphous and polycrystalline structures. The kinetics of crystal growth could influence the dominant crystal orientation. Fast-growing planes were not the most thermodynamically stable, but were kinetically controlled under the film growth condition. Oxidizing the sample in O2 atmosphere made the AlOx film grow in random directions. The excess oxygen was chemisorbed at the interface between AlOx and ZnO. Therefore, the neighboring oxygen–oxygen distance of AlOx and that of ZnO on their closest-packed planes seriously mismatched. At high power, the particles arrived at the substrate with high kinetic energy and high rate, which led to low density due to porous structure. The transmission decreased with an increase of the pores and surface roughness of AlOxfilm on ZnO-deposited glass. However, the diffusion of oxygen into the grains improved transmission when the sample was oxidized in O2 atmosphere.