Microstructure dependence of ZnO:Al films on the deposition conditions and the surface morphology of silicon substrate

The microstructure of ZnO:Al films prepared under different conditions on silicon wafers was investigated by means of diffraction analysis and high-resolution transmission electron microscopy. It was found that the structure feature of the films is strongly dependent on the preparation conditions. The films obtained in a transition mode (higher oxygen partial pressure) show a structure of well-developed columnar grains with a defined texture with c-axis vertical to the substrate surface that can be in different orientations. These grains nucleate directly on the amorphous surface of the substrate and grow with a nearly unchanged lateral dimension through the full film thickness. The films obtained in a metallic mode (lower oxygen partial pressure) consist of randomly oriented grains. A thin nanocrystalline layer was observed close to the interface. Some grains with columnar feature are found to develop during the later stages of the film growth. The dependence of the film structure on the growth conditions is discussed in terms of surface energy of the sample system.