Preparation and characteristics of ZnO films with preferential nonpolar plane orientation on polar sapphire substrates

The properties of ZnO thin film on sapphire (0001) substrate fabricated by single source chemical vapour deposition (SSCVD) method are studied. X-ray diffraction (XRD) analysis demonstrates that the film exhibits hexagonal structures but with preferential nonpolar (100) plane orientation, which is different from the crystalline structure of substrate, and its formation mechanism is also analyzed. The film has the characteristic of p-type conductivity originating from excess of oxygen, and its p-type conductivity is comparatively stable due to its nonpolar plane orientation. A strong ultraviolet (UV) emission and a high light transmission in visible wavelength region are observed from photoluminescence (PL) spectrum and transmittance spectra at the room temperature, and the strong ultraviolet emission originates from the recombination of free and bound excitons. Compared with the ZnO film on silicon substrates, the exciton emission peaks of the film on sapphire substrate show a slight blue shift about 50 meV, which might be related to the different crystallite sizes or surface stress of the films.