Effect of annealing treatment on optical and electrical properties of ZnO films

The ZnO-Al films were prepared by R. F. magnetron sputtering system using a Zn-Al target (with purity of 99.99%). The obtained films were characterized by X-ray diffraction, SEM and optical and electrical measurements. The experimental results show that the properties of ZnO films can be further improved by annealing treatment. The crystallinity of ZnO films becomes better, and the optical gap energy is decreased, but thermoelectric power is enhanced after heat treatment. The optical gap energy decreases from 3.75 eV to 3.68 eV when the annealing temperature increases from 25 ℃ to 400 ℃. This can be ascribed to the decrease of carrier concentration, resulting in Burstein shift.