Realization of highly conductive Ga-doped ZnO film with abnormally wide band-gap using magnetron sputtering by simply lowering working pressure

Sputter growth of highly conductive Ga-doped ZnO films with abnormally wide band-gap (E-g) is discussed in detail, as well as the accompanying defect behavior. It was observed that the optical Eg and the conductivity increased as the working pressure of the Ar plasma decreases. The ZnGaO films with E-g of 3.95 eV and resistivity of 2 x 10(-4) Omega cm was obtained by simply lowering the working pressure to 0.3 Pa, which represent the highest Eg value so far reported for the ZnO-based transparent conducting materials with a resistivity lower than 10(-3) Omega cm. It was proposed that this phenomenon may be attributed to the improved crystalline quality and the increased amount of the Ga incorporation into the Zn sites and the oxygen vacancy concentration. It was also suggested that the oxygen vacancy acts as the electron donor for the sputtered ZnO and ZnGaO films. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.