In this study, the high quality GaN films have been prepared by a simple, green and low-cost plasma enhanced chemical vapor deposition (PECVD)method at 950 ℃, with Ga2O3 and N2 as gallium source and nitrogen source, respectively. In order to improve the crystal quality of GaN films and figure out the photorespone mechanism of GaN films, the effect of the preparation temperature of GaN buffer layer on the crystal quality and photoelectric properties of GaN thin films was investigated. It is indicated that with the increase of the buffer temperature of GaN films, the crystal quality of GaN films increases first and then decreases, and the highest crystal quality is obtained at 875 ℃. When buffer layer temperature is 875 ℃, the calculated total dislocation density is 9.74?109 cm-2,and the carrier mobility is 0.713 cm2/V·s. After annealing, the crystal quality of GaN film have been improved. The total dislocation density of GaN film decreases to 7.38?109 cm-2,and the carrier mobility increases to 43.5 cm2/V·s. The SEM results indicate that GaN film (buffer layer temperature at 875 ℃) has smooth surface and compact structure. The Hall and XPS results indicate that there are N vacancy, Ga vacancy or O doping in the GaN film, which act as deep level to capture photogenerated electrons and holes. With increasing the bias, the photoresponsivity of the GaN film photodetector gradually increases and then reaches saturation. This is due to the deep levels produced by vacancy or O doping. In addition, photocurrent response and recovery of GaN film are slow, which also due to the deep levels formed by vacancy or O doping. At 5V bias, the photoresponsivity of GaN film is 0.2 A/W, and rise time is 15.4 s, and fall time is 24 s. Therefore, the high quality GaN film prepared by the proposed green and low-cost PECVD method present a strong potential of application in ultraviolet photodetector. The PECVD method developed by us provides a feasible way for the preparation of high quality GaN films, and the understanding of the photoresponse mechanism of GaN films provides a theoretical basis for the wide application of GaN films.
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