The Exploration On Electroluminescence Of ZnO Thin Films

Zinc Oxide is a wide-band-gap semiconductor material with the direct band gap of 3.37eV and the exciton binding energy of 60meV at room temperature, which has unique features of emitting ultraviolet light, furthermore, ZnO has been widely concerned for emitting blue or green light due to various point defects. Electroluminescence is a class of solid luminous phenomenon which electrical energy is directly converted to luminous energy, electroluminescent devices have been widely applied into illumination and flat-panel displays fields for its luminescence, fast response, low energy consumption, light weight, low cost, simple device structure and so on. This article employed sol-gel methods to prepare ZnO thin films and research on its structural, optical transmittance, surface morphology and photoluminescence properties. In addition, ZnO thin films electroluminescent devices were fabricated by using traditional metal-semiconductor device structure and the observed luminescence was carried out. Recent progress of ZnO electroluminescence, electroluminescent principle and choice of device materials were described and all the experimental process was presented in detail in the paper.X-ray diffraction(XRD) , scanning electron microscopy(SEM) and UV-VIS-NIR scanning spectrophotometer analysis were used to investigate the effect of sol concentration of different stirring times on the crystallinity, surface morphology and the optical transmittance of the films, the results indicate that ZnO thin films prepared by 60min sol of uniformly stirring are much better and present C-axis preferred orientation, dense uniform of surface, the size of nanoparticles is about 32nm. In addition, the optical transmittance in the visible regions is as high as 90%. The effect of different annealing temperatures from 400℃to 700℃on structural, optical and photoluminescence properties of ZnO films prepared by 60min sol of uniformly stirring is investigated, the results show that the values of FWHM for ZnO (002) diffraction peak decrease from 400℃to 600℃and then increase slightly at 650℃, the value of FWHM of ZnO (002) diffraction peak of ZnO films annealed at 600℃is minimum and its value is 0.229°. The optical transmittance of samples annealed between 400℃and 600℃is better and is high(>70%) in the range of 450nm-800nm according to the optical transmission spectrum. The samples which were annealed between 450℃and 550℃have strong ultraviolet emission peak, whereas, visible light emission intensity is weak while the UV emission peak intensity of the samples annealed from 600℃to 700℃is relatively weak but visible light emission intensity strong, so, emission peak intensity in different regions could be appropriately changed by choosing different annealing temperatures. The checking on the electroluminescence of ZnO thin films with MS structure is carried on, by naked eyes and PR650 spectral photometer respectively. The observed result is discussed finally.