Highly conducting transparent thin films based on zinc oxide

Doped zinc oxide thin films were prepared by rf magnetron sputtering using the dopants Al, Ga, In, and Ge. The best results were obtained with Al and Ga doping where room temperature conductivities were as high as 1600 and 1800 ohm^-1cm^-1, respectively. Hall measurements were performed at 77 K and 298 K. The Hall mobility as in the range of 9 to 22 cm²/Vs, and there was generally very little temperature dependence of the mobility or conductivity. Cation doping levels were as high as 10 at. %, but the conductivities did not increase beyond 3 at. % doping level. For films with high conductivity, electron carrier concentrations from Hall measurements were significantly lower than the concentrations of dopants. Optical measurements on the films showed that the average transmittance though the visible range is higher than 85%. The measurements also indicated a blueshift of the absorption edge with doping.