Plasma-assisted molecular beam epitaxy was used to grow thin films of ZnO on c-plane sapphire substrates. The crystalline properties of the layers as measured by x-ray diffraction were found to improve with lower growth temperatures, where the full width at half maximum (FWHM) of the (0002) peak x-ray rocking curves was shown to be in the range of 100 to I 100 arc sec. The surface roughness and crystalline quality were shown to be dependent on the Zn/O flux ratio. The electronic properties were found to be improved for higher growth temperatures with carrier concentrations in the range of 1 X 10(17) -5 X 10(18) cm(-3) and electron mobilities ranging from 80 to 36 cm(2)/Vs. P-type doping of the ZnO films was accomplished by introducing nitrogen into the oxygen plasma with resulting carrier concentration and hole mobility of 2.8 X 10(18) cm(-3) and 9 cm(2)/Vs, respectively. (c) 2005 American Vacuum Society.