Al-doped ZnO (AZO) films were prepared by an Ar:$H_2$ gas radio frequency (RF) magnetron sputtering system with a AZO ($2;wt{cdot}%;Al_2O_3$) ceramic target at the low temperature of $100^{circ}C$ and annealed in hydrogen ambient at the temperature of $300^{circ}C$. To investigate the influence of the $H_2$ flow ratio on the properties of the AZO films, the $H_2$ flow ratio was changed from 0.5% to 2%. As a result, the AZO films, deposited with a 1% $H_2$ addition, showed a resistivity of $11.7;{ imes};10^{-4};{Omega}{cdot}cm$. When the AZO films were annealed at $300^{circ}C$ for 1 hour in a hydrogen atmosphere, the resistivity decreased from $11.7;{ imes};10^{-4};{Omega}{cdot}cm$ to $5.63;{ imes};10^{-4};{Omega}{cdot}cm$. The lowest resistivity of $5.63;{ imes};10^{-4}{Omega}{cdot}cm$ was obtained by adding 1% hydrogen gas to the deposition and annealing process. The X-ray diffraction patterns of all the films showed a preferable growth orientation in the (002) plane. The spectrophotometer measurements showed that the transmittance of 85% was obtained by the film deposited with the $H_2$ flow ratio of 1% at 940 nm for GaAs/GaAlAs LEDs.