Synthesis and Characterization of Cu-doped ZnO Film in Nanowire like Morphology Using Low Temperature Self-Catalytic Vapor-Liquid-Solid (VLS) Method

摘要

Cu-doped ZnO film in nanowire structure is synthesized by a closed space flux sublimation and periodic oxidation method at ～300°C over Si substrate. Oxidative process controlled self-catalytic VLS mechanism is proposed for the film growth. X-ray diffraction pattern establishes that Cu-doped ZnO nanowires retain the crystallite structure of the wurtzite ZnO. TEM studies indicate single crystal character of the Cu-doped ZnO nanowires. Optical absorption analysis of Cu-doped ZnO nanowires defines two direct energy band gaps. The low energy band gap at 3.2eV is intrinsic to the Cu-doped ZnO material. The higher energy band gap at 3.5eV is attributed to the nanosize, mediated by strong forward scattering of light from the nanowires. Sharp photoluminescence in Cu-doped ZnO corresponding to near bandgap free exciton emission is observed and a redshift of ～0.07 eV is consistent with the effect of Cu-doping. The visible emission band in both ZnO and Cu-doped ZnO shows a broad green emission band with Cu-substitution shifting the maximum visible luminescence towards the higher energy side.