As-doped ZnO films were grown by the radio frequency magnetron sputtering method. As the substrate temperature during growth was raised above ϳ400°C, the films changed from n type to p type. Hole concentration and mobility of ϳ6 ϫ 10 17 cm −3 and ϳ6 cm 2 V −1 s −1 were achieved. The ZnO films were studied by secondary ion mass spectroscopy, x-ray photoelectron spectroscopy ͑XPS͒, low temperature photoluminescence ͑PL͒, and positron annihilation spectroscopy ͑PAS͒. The results were consistent with the As Zn -2V Zn shallow acceptor model proposed by Limpijumnong et al. ͓Phys. Rev. Lett. 92, 155504 ͑2004͔͒. The results of the XPS, PL, PAS, and thermal studies lead us to suggest a comprehensive picture of the As-related shallow acceptor formation. Downloaded 21 Oct 2010 to 147.8.21.59. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 073709-3 Fan et al. J. Appl. Phys. 106, 073709 ͑2009͒ Downloaded 21 Oct 2010 to 147.8.21.59. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 073709-5 Fan et al. J. Appl. Phys. 106, 073709 ͑2009͒ Downloaded 21 Oct 2010 to 147.8.21.59. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 073709-6 Fan et al.

Arsenic-doped ZnO films were fabricated by radio frequency magnetron sputtering method at a relatively low substrate temperature of 200 C. Post-growth annealing in air was carried out up to a temperature of 1000 C. The samples were characterized by Hall measurement, positron annihilation spectroscopy (PAS), secondary ion mass spectroscopy (SIMS), and cathodoluminescence (CL). The as-grown sample was of n-type and it converted to p-type material after the 400 C annealing. The resulting hole concentration was found to increase with annealing temperature and reached a maximum of 6 Â 10 17 cm À3 at the annealing temperature of 600 C. The origin of the p-type conductivity was consistent with the As Zn (V Zn) 2 shallow acceptor model. Further increasing the annealing temperature would decrease the hole concentration of the samples finally converted the sample back to n-type. With evidence, it was suggested that the removal of the p-type conductivity was due to the dissociation of the As Zn (V Zn) 2 acceptor and the creation of the deep level defect giving rise to the green luminescence. V

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