P-type ZnO films with c-axis orientation deposited by DC reactive magnetron sputtering are first reported in this paper. ZnO films were prepared in NH3-O-2 atmosphere (ammonia concentration varied from 0% to 67%) with the substrate temperature in the range of 400-550degreesC. The properties were examined by X-ray diffraction, atomic force microscopy, Hall measurement, spreading resistance processing and optical transmission spectra. Results showed that excess zinc and interstitial hydrogen play important roles in the doping process. The N-doped ZnO film deposited on alpha-Al2O3 (0 0 0 1) at a substrate temperature of 500degreesC and an ammonia concentration of 50% showed p-type conduction with good electrical properties. A carrier density of 3.2 x 10(17)cm(-3) and resistivity of 35 Omega cm were observed. The p-type ZnO films possess a transmittance of about 90% in the visible region and a band gap of 3.21 eV at room temperature. In addition, ZnO p-n homojunctions on p-Si(1 0 0) substrate (p-ZnO:N/n-ZnO/p-Si) have also been first achieved, which could further open the door for practical applications in diverse optical devices. (C) 2003 Elsevier Science B.V. All rights reserved.