Effects of post-annealing temperature on structural, optical, and electrical properties of ZnO and Zn1−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 °C. The crystallinity of ZnO film grown at 600 °C was significantly improved by annealing treatment while the film grown at 700 °C showed little improvement with annealing. The near band edge emission peak of ZnO films grown at 600 and 700 °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 °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 °C. The ZnO film grown at 600 °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 °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.