氧气后处理对氧化锌薄膜紫外发射性质的影响

为了提高ZnO光发射效率和制备p型ZnO,对热处理的氧分压对薄膜的结构、形貌、光致光发射和ZnO/Si异质结的Ⅰ-Ⅴ特性的影响进行了研究.用直流反应溅射法在p型硅衬底上生长ZnO薄膜形成n-ZnO/P-Si异质结.在1000℃下用不同比例的氧和氨热处理,我们发现,在纯氮气中得到的样品有强的紫外发射(390nm),随氧气比例增大,紫外增强,同时绿光也产生并随之增强.但过大的氧分压反而产生多的受主缺陷,使越来越多的激发能量转移到发射能量低的绿光中心,从而使紫外减弱.在纯氧和无氧条件下热处理的俄歇谱表明纯氧下氧过量,而无氧下锌大大过量.ZnO/p-Si异质结的Ⅰ-Ⅴ特性表明,无氧热处理表现为典型的n-ZnO/p-Si异质结;而在纯氧气氛中处理后所得Ⅰ-Ⅴ曲线反向,这表明在高氧压下受主缺陷的产生,表明ZnO薄膜有可能由于高氧压热处理由n型转为p型.

Influence of Oxygen Annealing on Ultraviolet Emission of ZnO Films

ZnO film is attracting more attention because of its ultraviolet emission at room temperature and its potential applications in ultraviolet photoelectron devices in recent years.For the applications preparation of good-quality ZnO films and strong ultraviolet emission in films are requested.Annealing in different ambiences is a good method to improve the quality and to change the stoichiometrical composition.ZnO films were prepared by direct current reaction sputtering and annealed in different oxygen partial pressures(P_O2).The laser lasing on the films was observed from the time resolution spectrum.X-ray diffraction analysis shows that the crystal constants decrease and the gain sizes of films increase with P_O2,these analysis and images of films by atom force microscopy show that the qualities of ZnO films were improved by annealing in oxygen ambiences.The influences of annealing P_O2 on photoluminescence(PL)and its relation to native defects were investigated also.We found that the intensities of ultraviolet photoluminescence were increased with oxygen partial pressures in certain range of P_O2 due to the improvement of the structure of films.But in higher P_O2,ultraviolet intensities decreased and green intensities increased instead.We suggest that more excitation energy was transferred to green center because of the generation of more acceptors in higher P_O2 that these acceptors act as green emission center in the films,the refore UV was decreased,green was increased.The compositions analyses in depth of samples A and E by Auger electron spectra show that A film(annealed in pure N₂ ambience)has stoichiometry of Zn]/O]>1 and Samples E(in pure O₂)has that of Zn]/O]<1,it indicates there are more donor defects in Sample A and more acceptors in Sample E.The I-V curves of the junctions Sample E indicates the more acceptors generated in the ZnO film and may inversed to p-type semiconductor due to annealing in higher P_O2.