Effects of post-annealing temperature on structural, optical, and electrical properties of ZnO and Znl-xMgxO films by reactive RF magnetron sputtering

ZnO and Zn1-xMgxO thin films were deposited on (0 0 0 1) sapphire substrates by a reactive RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated over the annealing temperatures from 400 to 800 degrees C. The crystallinity of ZnO film grown at 600 degrees C was significantly improved by annealing treatment while the film grown at 700 degrees C showed little improvement with annealing. The near band edge emission peak of ZnO films grown at 600 and 700 degrees C appeared at 3.26 eV after thermal annealing, which was not observable in as-grown film. The ratio of near band edge emission intensity to deep level emission intensity increased with annealing temperatures below 700 degrees C but thereafter decreased. The optical transmittance in the visible region was not influenced much by annealing treatment, showing around 85% for both as-grown and annealed films. The annealed ZnO films exhibited an n-type characteristics whereas high insulator characteristics were observed for as-grown samples. The superior carrier concentration, mobility, and resistivity were achieved with an annealing treatment. An optimum annealing treatment was found to be at 600 degrees C. The ZnO film grown at 600 degrees C followed by the optimum post annealing shows the most improved structural, optical, and electrical properties even better than those of the film grown at a higher growth temperature (700 degrees C) with post-annealing. With Mg doping into ZnO film, blue shift of 150-200 meV was observed, depending on the annealing temperature. The reactive RF magnetron sputtering coupled with an optimum annealing treatment would provide a promising and economically feasible method for optoelectronic device fabrication. (c) 2005 Elsevier B.V. All rights reserved.