Dependence of the resistivity and the transmittance of sputter-deposited Ga-doped ZnO films on oxygen partial pressure and sputtering temperature

Ga-doped ZnO (GZO) thin films were prepared by rf magnetron sputtering and dependence of the electrical resistivity and the transmittance of the GZO films on the oxygen partial pressure (R = the O₂/Ar gas flow ratio) and the substrate temperature were investigated. The resistivity of the GZO film decreases first and then increases with an increase in the substrate temperature (T). A minimum resistivity obtained with a substrate temperature of 300 °C is 3.3 × 10^-4 cm. The resistivity nearly does not change with R for R < 0.25. The decrease in the resistivity for R < 0.25 is attributed to enhancement in crystallinity, whereas the increase in the resistivity for R > 0.25 to precipitation of gallium oxides at grain boundaries. Optical transmittance of the GZO films is enhanced by increasing R up to 0.75. This enhancement in the transmittance is due to a decrease in oxygen vacancy concentration and a decrease in surface roughness with R.