Preparation and characterization of gallium-doped zinc oxide thin films

Abstract

Transparent conductive Ga-doped ZnO (GZO) thin films have been deposited on soda-lime glass substrates by RF magnetron sputtering at various Ga₂O₃ con¬tents and sputtering conditions. Sintered ZnO with various Ga₂O₃ contents of 2, 3, 4 and 6 wt% were prepared as targets. The RF power was varied from 50 W to 125 W. At the RF power of 100 W, the Ar pressure was also varied in a narrow range from 6.0X10⁻³ mbar to 1.0X10⁻² mbar. The effects of Ga doping and sputtering conditions on the structural, electrical and optical properties were in¬vestigated by X-ray diffraction, Hall measurement and optical transmission in the UV/VIS/NIR range, respectively. It was found that the films become poor crys-tallinity and their electrical resistivity decrease with increasing RF power for a given Ga₂O₃ content and Ar pressure. Both mobility and carrier concentration increase due to the increase of donor defects. When Ar pressure was varied, the resistivity differs insignificantly. The carrier concentration and free carrier absorption in the long wavelength increase with more Ga doping. Consequently, the resistivity and optical transmission decrease while the energy gap widens with increasing Ga₂O₃ content at the same sputtering condition.