Study On The Laser Synthesis And Laser Irradiation Effect Of Zinc Oxide Nano-Materials

As a wide band-gap semiconductor material with large exciton binding energy at room temperature, Zinc oxide is a promising candidate for UV emitting material, optoelectronic devices, LED and LD, et al. Recently, with the development of nano-technology and requirement of micro device, the investigation on preparation of ZnO nano-materials and the excellent photoelectric property have gained substantial interest among the researchers.In this thesis, the laser technique was used as the main tool not only for the preparation of ZnO nano-materials, but also for the improvement of physical properties. Firstly, we prepared ZnO films on sapphire substrate by pulsed laser deposition technique. The effect of the growth conditions such as deposition temperature, oxygen partial pressure on the properties of ZnO films was discussed in detail; accordingly, the optimized growth parameters of ZnO film were obtained. Secondly, we focused on the investigation of the effect of laser irradiation on the properties of ZnO film. It was found that the UV photoluminescence intensity could be increased sharply after the irradiation of excimer laser withλ=248 nm, accompanying with the enhancement of electrical conductivity by three orders of magnitude. And also, under laser irradiation, the melting grain connected with each other, leading to the decrease of surface roughness and increase of grain size. It is suggested that the photochemical and heat effect exist simultaneously when the KrF laser irradiated the ZnO film. The enhancement of electrical conductivity and UV photoluminescence intensity are mainly due to the influence of photochemical effect. When irradiated, the phonon energy of the KrF excimer laser is sufficiently high to break Zn-O bonds. Therefore, a great deal of Vo formed by the evaporation of oxygen atoms into ambiences, which acting as shallow donor level. Combined with the laser irradiation results, we suggested the origin of UV emission at room temperature is mainly the recombination of neutral donor (Vo) bound exciton. However, the heat effect resulted in the changes of surface morphology: larger grain size and lower surface roughness. What's more, the ZnO nanoparticles were prepared using the method of pulsed laser ablation with Nd:YAG laser (1064 nm). These nanoparticles with size ranging from 50 to 100 nm showed good UV emission at room temperature. The photoluminescence properties of silver nanoparticles with different size were studied, which were prepared using YAG and KrF laser as ablation sources, respectively. And also, the mechanism of pulsed laser ablation for nanoparticles was discussed.