Improved crystallinity and optical properties of AlO_x thin films by a ZnO interlayer

To ascertain how the substrate influences the quality of AlO_x films, AlO_x films were grown on a bare glass and a ZnO-deposited glass in this study. By applying a ZnO interlayer before the AlO_x deposition, AlO_x films exhibited polycrystalline structure rather than amorphous as obtained by sputtering on a bare glass. For AlO_x film on the ZnO-deposited glass, the transmission electron microscopy observation showed the coexistence of amorphous and polycrystalline structure, which reveals that the (122) plane in AlO_x film is parallel to the surface of the substrate. The grains of the AlO_x film grown on a ZnO-deposited glass comprising many small crystallites aggregated with sizes varying between 38 and 54 nm with irregular grain shapes. Besides, the ZnO interlayer with different deposition parameters had a significant effect in the diffusion interface between AlO_x and ZnO. The ZnO interlayer could improve the optical transmission of AlO_x films, especially when ZnO films are prepared with a high power of 200 W. Therefore, the glass/ZnO may be a good alternative substrate for producing high-quality AlO_x films by controlling the epitaxial grain growth. The AlO_x films grown on ZnO-deposited glasses have very good qualities in terms of crystallinity and optical properties.