High conductivity in gallium-doped zinc oxide powders

Gallium-doped zinc oxide powders have been prepared with electrical conductivities at 25 °C as high as 300 Ω^-1 cm^-1, more than 1000 higher than previously reported. All materials prepared can be represented as Zn_1-xGa_xO, Zn_1-yGa_yO_1+(y/2), or a combination of these two. For Zn_1-xGa_xO, the room-temperature conductivity increases monotonically with increasing x up to 2.7%, which is the limit of Ga solubility for this formulation at our synthesis temperatures of 1000 to 1200°C. Conductivities measured from 4.2 to 500 K showed only a very small temperature dependence. An ESR peak (g = 1.96), attributed to the conduction electrons, broadens with increased doping level. The hexagonal unit-cell edges increase with increasing x over the entire range of x. For the low conductivity Zn_1-yGa_yO_1+(y/2) series, the level of Ga substitution can reach at least 4.0%.