Radio-frequency superimposed direct current magnetron sputtered Ga:ZnO transparent conducting thin films

Abstract

The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputtering deposition on the properties of gallium doped ZnO (GZO) based transparent conducting oxides has been examined. The GZO films were deposited using 76.2 mm diameter ZnO:Ga2O3 (5 at. % Ga vs. Zn) ceramic oxide target on heated non-alkaline glass substrates by varying total power from 60 W to 120 W in steps of 20 W and at various power ratios of RF to DC changing from 0 to 1 in steps of 0.25. The GZO thin films grown with pure DC, mixed approach, and pure RF resulted in conductivities of 2200 ± 200 S/cm, 3920 ± 600 S/cm, and 3610 ± 400 S/cm, respectively. X-ray diffraction showed all films have wurtzite ZnO structure with the c-axis oriented perpendicular to the substrate. The films grown with increasing RF portion of the total power resulted in the improvement of crystallographic texture with smaller full-width half maximum in χ and broadening of optical gap with increased carrier concentration via more efficient doping. Independent of the total sputtering power, all films grown with 50% or higher RF power portion resulted in high mobility (∼28 ± 1 cm2/Vs), consistent with observed improvements in crystallographic texture. All films showed optical transmittance of ∼90% in the visible range.