Properties of gallium-doped ZnO deposited onto glass by spray pyrolysis

Gallium-doped ZnO (GZO) thin films were obtained for the first time onto glass by the spray pyrolysis process, using zinc acetate and gallium pentanedionate as precursors. The role of Ga/Zn atomic ratio, in the starting solution, and the substrate temperature were investigated and the optimum deposition conditions have been outlined. The undoped ZnO thin films were prepared using a 0.05 M zinc acetate dihydrate r.g. solution dissolved in methanol. Gallium doping was achieved by adding a 0.3 M gallium pentanedionate dissolved in pentanedione. A solution flow rate of 1.5 ml/min and a gas flow rate of 6 l/min @ 1 bar were used for the deposition of the films. The films are very uniform with no haze or visible clusters. The electrical and optical properties are enhanced as substrate temperature and Ga/Zn ratio are increased. The films show an n-type electrical resistivity as low as 4.9 x 10(-2) Ohm cm with a carrier concentration as high as 1 x 10(20) cm(-3). Average optical transmission on the whole visible range as high as 85% for the best conductive films has been obtained. Refractive index of layers is modified by the growth temperature and indium doping. Haacke's figure of merit up to 3 x 10(-4) Ohm(-1) in a 500 nm thick films was obtained. The electrical and optical properties of ZnO:Ga thin films had shown that this semiconductor has a big potential to use like a transparent conductor oxide in a solar cell structure. (C) 1998 Elsevier Science B.V. All rights reserved.