Influence of Vacuum Annealing on Structural, Optical, Electrical, and Magnetic Properties of Zn$_{0.94}$Co$_{0.05}$Al$_{0.01}$O Diluted Magnetic Semiconductor Thin Films

Abstract

The Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.94</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.01</sub> O diluted magnetic semiconductor (DMS) thin films were made by rf magnetron co-sputtering, and annealed in vacuum at 500°C (for 0, 20, 40, and 80 min, respectively). The films have a single ZnO wurtzite structure with -axis preferred orientations, without any segregated secondary phase, and Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions substitute tetrahedrally coordinated Zn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions site. The as-grown film is insulating and in a state of tensile stress parallel to the c-axis. After annealing in vacuum, the films have tensile stresses parallel to the (002) plane, and become conductive; moreover, the carrier concentrations increase with increasing the annealing time. The as-grown film possesses the room-temperature ferromagnetism (RTFM) and the saturation magnetization (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) is 0.8 μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> /Co. As the film is annealed in vacuum, the value of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> is reduced first then enhanced with the increase of annealing time.