Various post-annealing treatments on aluminum doped zinc oxide films fabricated by ion beam co-sputtering

摘要

Aluminum doped zinc oxide (AZO) films with the aluminum concentration of 1.5 at.% were fabricated by co-sputtering dual metallic targets, Al and Zn, under the oxygen partial pressure of 1.3 ×10~(-4) torr. The total pressure was kept at 2.3 ×10~(-4) torr during the deposition. The poly-crystalline structure, optical property and conductivity of the films were investigated by XRD, UV-VIS-IR spectrometer and Hall measurement, respectively. The more intense ZnO crystallinity of (002), larger grain size, smaller d-spacing and highest carrier concentrations were observed on the as-deposited AZO film which had the lowest resistivity of 7.8 ×10~(-4) Ωcm. Comparing the AZO films post-annealed in atmosphere, in vacuum and in hydrogen ambiance, the structures processed in vacuum and hydrogen ambiance remained the good ZnO crystallinity in the film resulting from the oxygen deficient state of the films after post-annealing processes. The better thermal stability of resistivity was observed in the films post-annealed in hydrogen ambiance due to the formation of the shallow donor in the film. Furthermore, the resistivity increased as increasing the post-annealing temperature in atmosphere. When the as-deposited film were post-annealed at temperature of 400 ℃, the resistivity was about more than two orders of magnitude than that of the as-deposited film resulting from the decrease of the donor concentration and mobility in the AZO film. The variation of the carrier concentration in the AZO film also shifted the energy band gap. However, the average visible transmittance of all AZO films in this study was above 80 % regardless of the deposition and post-annealing conditions.