Effect of rapid thermal annealing on microstructure, electrical properties, and optical properties of Al-doped ZnO sol–gel deposited thin films

Aluminum (Al)-doped ZnO thin films were prepared on glass substrates by sol–gel spin coating method. After the ZnO thin films were densified and crystallized by rapid thermal annealing (RTA), their microstructures, electrical properties and optical properties were studied. Following RTA treatment at various temperatures, the microstructure and surface morphology of the films were characterized by X-ray diffraction and scanning electron microscopy, respectively. Resistivity was measured at varying RTA temperatures by four-point probe technique. Diffusion of the Al reduced the resistivity of the ZnO:Al thin films to 3.15 × 10−3 Ω cm. Atomic force microscopy further showed that, after RTA treatment, Al diffusion into the ZnO films and grain growth roughened the surface of the films. The effects of temperatures of the RTA process on the structural, electrical, and optical characteristics of the ZnO:Al thin films are analyzed and discussed.