| Zinc oxide (ZnO) is a direct wide band-gap semiconductor material with band gap of3.4eV, the large exciton binding energy of60meV, which is higher than other wide band gap materials such as GaN (21meV) or ZnSe (20meV), also higher than thermal energy (26meV) at room temperature, high exciton emission efficiency of320cm-1. ZnO films have attracted the intense interest for its great potential applications in the optically transparent conducting layers as the electrode for thin-film solar cells.To realize the application of ZnO in optoelectronic devices, excellent epitaxy n-and thin films are necessary. Based upon that, fabricating the ZnO homojunction. The formation energy of the intrinsic defects (Zni and Vo) is very low, so there is a heavy compensation in the p-type doping, which makes difficult to chang into p-type ZnO.with the dopant(A1,In,Ge), we have the ability to make high quality n-type ZnO thin films; while the fabrication in a reproducible and stable way of a p-type material, which would satisfy device requirements, remains still a technological challenge. Among possible acceptor dopants, nitrogen is a good candidate for producing a shallow acceptor level in ZnO films, and simultaneously codoping using donor (such as Ga, In, Al) and acceptor (N) in ZnO can be expected to enhance the solubility of nitrogen and give rise to a shallower N-acceptor level in the band gap. Based on the codoping theory which has been actively studied in recent years, in the present dissertation, N-Al codoped p-type ZnO films on quartz glass substrates using RF magnetron sputtering technology combining with the direct implantation of N+ions are prepared successfully.The effects of thermal annealing on the structure, electrical and optical properties of the ZnO films are investigated by x-ray diffraction (XRD) via a Philips MRD system with Cu Kα radiation (λ=0.1540597nm), the Ecopia HMS-3000Hall measurement system and transmission spectrum. The experimental results suggest that an appropriate annealing temperature and time play an important role in the microstructure, electrical and optical properties, especially the types of conduction of ZnO films. When the annealing temperature is in the range of500-600℃and annealing time changes from3 to10min, N-Al codoped p-type ZnO films can be obtained. It is noticeable that the film annealed for8min at578℃exhibits the optimal p-type electrical properties with hole concentration of5.66×1018cm-3, hall mobility of0.53cm2V-1s-1, and low resistivity of about2.08Ωcm, as well as good film quality among all the samples. At last, to offer much more reference to optimizing the procedure of fabricating the p-type ZnO films, we draw a picture that shows the distribution of conversion of p-type conduction in our experiment.X-ray photoelectron spectroscopy analysis confirmed the presence of nitrogen and indium in the form of N-Zn bond and N-Al bond in the codoped films, and the incorporation of aluminium causes the change in the chemical state of nitrogen, which promotes the formation of p-type conduction,and the p-type conductivity of ZnO is attributed the formation of the Alzn+2No complex. |
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