Al, Mg Co-doped ZnO thin films: Effect of the annealing temperature on the resistivity and ultraviolet photoconductivity

Interesting electrical and optical properties can be obtained from sol-gel doped Zinc Oxide (ZnO) materials by controlled introduction of dopants in the precursor solution. In this work we investigate the effects of annealing temperature on Al and Mg co-doped ZnO thin films. All samples were dip coated from the same solution, using identical techniques and pre-heating temperature, but were annealed in air at various temperatures ranging from 500 degrees C to 650 degrees C. A three-order magnitude reduction in electrical resistivity was achieved for an increase of 100 degrees C annealing temperature. The structural properties and the energy band-gap remained relatively unchanged during this process. Photocurrent measurements carried out using an ultraviolet excitation source indicate a 5x increase in magnitude, along with increase in persistence behavior. The mechanism behind these effects has been linked to temperature-induced variation in Mg to Al ratio in the films, measured using energy dispersive spectroscopy. Our results indicate that strong in-plane variation of resistivity in ZnO thin films can be carried out using localized heating, opening the way to simpler fabrication processes.

Automated summary

The effects of annealing temperature on Al and Mg co-doped ZnO thin films were investigated. It was found that a three-order magnitude reduction in electrical resistivity was achieved for an increase of 100 degrees C annealing temperature, and a 5x increase in magnitude of the photocurrent was observed. The mechanism behind these effects was attributed to the temperature-induced variation in Mg to Al ratio in the films.