Al-N co-doped p-type ZnO thin films have been grown in N2O-O-2 atmosphere. Types of conduction, carrier density and mobility in as-grown films were found to be dependent on N2O partial pressure ratios. The highest hole density was found to be 8 x 10(17) cm(-3), with the lowest carrier mobility of 0.1 cm(2) V-1 s(-1) and the best crystallinity for the films deposited in pure N2O ambient. Results show that it's difficult to achieve p-ZnO with both high hole concentration and high mobility by co-doping, most likely due to the inherent defects of the AIN precipitates produced in co-doping process. As-grown ZnO films show good transparency of about 90% in the visible range. A decrease in optical band gap for co-doped p-type ZnO was observed. (C) 2004 Elsevier B.V. All rights reserved.