| As one kind of direct wide band gap semiconductors, ZnO has many excellent optical and electrical properties and it is a promising material for using in ultraviolet light-emitting diodes, laser diodes and photodetectors. In this paper, ZnO thin films were deposited in the pulsed laser deposition (PLD) system by using KrF excimer laser. The deposition of the films and their optical and electrical properties were systemically studied.The primary points are as follows:1. The ZnO films were prepared on silicon substrates at different substrate temperatures and oxygen pressures. The photoluminescence spectrum and X-ray diffraction pictures of the films which were deposited at the substrate temperature of 400℃and the oxygen pressures of 10-3Pa to 10Pa were taken. The results suggest that the films deposited at 400℃and 10-2Pa have the strongest ultraviolet emission intensity. But the results of the films deposited at higher substrate temperature (700℃) and oxygen pressures (10Pa -100Pa) indicate that the film have the strongest ultraviolet emission intensity when it was deposited at 700℃and 100Pa. We can find that oxygen pressure and substrate temperature have important influences on the optical properties of ZnO thin films. In a word, these two parameters should be considered comprehensively so as to get ZnO thin films with strong ultraviolet emission intensity, and the oxygen pressure should be increased corresponding to the higher substrate temperature. We can find from the further study that the films with the best crystallinity can be made at 10-1Pa, while the films with the strongest photoluminescence intensity were made at 10-2Pa. Considering the different oxygen pressures for the films, we came to a conclusion that the intensity of ultraviolet emission not only depends on the crystallinity, but also on the stoichiometry of the thin film.2. We had a research on the effect which the defects in ZnO thin films have on the intensity and the energy position of the peak for deep-level(DL) emission. (1) The PL spectrum of DL emission can be divided into three bands: the blue luminescence band (470nm), the green luminescence band (515nm-540nm) and the yellow luminescence band (609nm). (2) Although it is generally considered that the intensity of DL emission increased as that of the UV emission decreased, we can find from our experimental results that they changed in the same way as the oxygen pressure increased. On one hand, the DL emission can be enhanced as the amount of the defects in the film increased which lead to much more defect energies. On the other hand, the location of the atomics around the defects can be affected and it may change more or less. The lattice relaxation induced by the defects leads to the multi-phonon related non-radiation transition of localized-state-electrons. As a result, the radiation of DL emission turned into the non-radiation, and the intensity was reduced.3. The films were deposited on glasses under the appropriate conditions. The photodetectors with planar electrode configuration and sandwiched electrode configuration were prepared, and the photoresponse properties of photodetectors with different configurations have been studied. The transient photocurrent of the samples revealed that the sandwiched electrode configuration photodetector with ITO transparent electrode can not only have shorter response time as the distance is small and controllable between the two electrodes, but also have larger responsibility as the ITO film has high transparent and external quantum ratio. |
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