Substitution mechanism of Ga for Zn site depending on deposition temperature for transparent conducting oxides

High quality transparent conductive gallium-doped zinc oxide (GZO) thin films were deposited on glass substrates using rf-magnetron sputtering system at the temperature ranging from room temperature (RT) to 500 degrees C. The temperature-dependence of Ga doping effect on the structural, optical and electrical properties in ZnO has been investigated. For the GZO thin films deposited at over 200 degrees C, (103) orientation was strongly observed by X-ray diffraction analysis, which is attributed to the substitution of Ga elements into Zn site. X-ray photoelectron spectroscopy measurements have confirmed that oxygen vacancies were generated at the temperature higher than 300 degrees C. This might be due to the effective substitution of Ga3+ for Zn site at higher temperature. It was also found that the optical band gap increases with deposition temperature. The optical transmittance of GZO thin films was above 87% in the visible region. The GZO thin films grown at 500 degrees C showed a low electrical resistivity of 4.50 x 10(-4) Omega cm, a carrier concentration of 6.38 x 10(20) cm (-3) and a carrier mobility of 21.69 cm(2)/V. (C) 2012 Published by Elsevier B.V.