Preparation Of Li,Mg Doped/Li-Mg Codoped ZnO Thin Film And ZnO-metal Schottky Diode

The interest in ZnO is fueled by its prospects in optoelectronics applications owing to its direct wide band gap (Eg-3.26eV at room temperature) and a large exciton binding energy (-60meV at 300k) which could lead to lasing action based on exciton recombination even above room temperature. In addition, ZnO also has advantage in structure, electrical and optical characters which could be used to the window of solar cells, air and humidity sensor, piezoelectricity sensor, UV detector and so on. This article consists of two parts:(1) Preparation of Li,Mg doped/Li-Mg codoped ZnO thin films by the method of sol-gel and the effect of Li and Mg doping on the structure, morphology and optical properties of ZnO thin film were studied. (2) Preparation of glass-AZO-ZnO-Ag Schottky diodes by magnetron sputtering, and the effect of annealing and substrate materials on the ZnO-Ag Schottky contacts were studied.The results showed that:(1)The crystallinity of Li-doped ZnO thin films were improved and the surface morphology of the films was affected from the lithium incorporation, while the effect of Mg doping on the crystallinity and surface morphology was not obvious. ICP-AES (Inductively Coupled Plasma) was used to quantify the Li+,Mg2+ and Zn2+ present in the ZnO films after preheating and annealing. The result showed that the mol% of Mg2+ and Zn2+ in the ZnO films was little changed while the mol% of Li+ deceased greatly after preheating and annealing. Compared to the undoped ZnO thin film, the optical transmittance of the Li-doped ZnO thin film is decreased as the surface of Li-doped ZnO thin films is rough while the absorption edge of Mg-doped ZnO thin film shifted toward shorter wavelength region. The undoped ZnO,Li-doped ZnO and Mg-doped ZnO thin films showed a dominent UV emission at～390 nm and Li-Mg codoped ZnO thin film showed another green emission centered at～500 nm. Finally, according to the certain mathematical relationship of the band gap and the optical transmittance of the films, the band gap were calculated and found that the Mg-doped ZnO thin film is about 0.64eV wider compared to undoped ZnO films. (2) The preparation of ZnO-metal Schottky diode prepared by the method of Magnetron sputtering and vacuum evaporation. The structure of the ZnO-metal Schottky diode was: glass/AZO film/ZnO thin film/Ag. The result showed that the AZO film as a buffer layer of ZnO film, can reduce the defects of the ZnO crystal structure resulting from the misfit lattice between ZnO film and glass to obtain relatively good quality ZnO films. TheⅠ/Ⅴcharacteristics of the contact on the ZnO-Ag showed that the diode with the structure:glass substrate/AZO thin films (AZO thin film annealed at 560℃for 1h)/ ZnO thin film/Ag can form a good Schottky contact with low saturation current However, in the absence of AZO thin film annealing, ZnO-Ag contacts can be formed the Schottky contact, but with obvious instability, for the breakdown can easily occur when increased the voltage.