Substrate dependence of preferred orientation in sol-gel-derived zinc oxide films

The preferred orientation of ZnO films synthesized by the sol-gel technique was investigated with increasing annealing temperature. Different substrates like soda-lime glass, quartz glass, Corning 7059 glass, polycrystalline Al₂O₃ and p-type Si(100) were used to examine the substrate effects on the growth of ZnO. The degree of orientation of the (002) plane in the films increased with temperature when the amorphous glass substrates were used. Highly oriented ZnO films along the (002) plane were obtained with soda-lime glass substrate at a particular temperature (550°C). Similar, but not so strong preference was obtained in case of Corning 7059 glass at higher temperatures. In case of the crystalline substrates, no such high degree of orientation was observed. These phenomena are considered in general terms to be closely related with the interfacial energy of the film and the substrate and especially in case of amorphous substrates, to the structure of the glass (presence or absence of non-bridging oxygens).