Improvement of the thermal and chemical stability of Al doped ZnO films

To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300 degrees C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO and SnO2 targets. Amorphous ZTO films had resistivity in the range from 10(-2) to 10(-3) Omega cm and were stable up to temperature of 400 degrees C. Heat treatments of bare AZO films in the atmosphere at 400 degrees C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments in the temperature range from 200 to 400 degrees C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors.