Electrical Properties of Gallium-Doped Zinc Oxide Films Prepared by RF Sputtering

Ga-doped polycrystalline ZnO films on glass substrates were prepared by sputtering the targets, which had been prepared by sintering disks consisting of ZnO powder and various amounts of Ga₂O₃, to investigate the effects of gallium doping and sputtering conditions on electrical properties. Optimizing the RF power density, argon gas pressure, and gallium content, transparent Ga-doped ZnO films with resistivity less than 10⁻³Ω·cm were obtained. Electron concentrations for undoped and Ga-doped ZnO films were on the order of 10¹⁸ and 10²¹/cm³, respectively. The Ga-doped ZnO films became degenerate when the electron concentration exceeded ∼ 10¹⁹/cm³, and the optical band gap increased with increasing carrier concentration because of the increase of Fermi energy in the conduction band.