Highly stable hydrogenated gallium-doped zinc oxide thin films grown by DC magnetron sputtering using H2/Ar gas

The effects of water partial pressure (PH2O) on electrical and optical properties of Ga-doped ZnO films grown by DC magnetron sputtering were investigated. With increasing PH2O, the resistivity (ρ) of the films grown in pure Ar gas (Ar-films) significantly increased due to the decrease in both free carrier density and Hall mobility. The transmittance in the wavelength region of 300-400 nm for the films also increased with increasing PH2O. However, no significant PH2O dependence of the electrical and optical properties was observed for the films grown in H2/Ar gas mixture (H2/Ar-films). Secondary ion mass spectrometry (SIMS) and X-ray diffraction (XRD) analysis revealed that hydrogen concentration in the Ar-films increased with increasing PH2O and grain size of the films decreases with increasing the hydrogen concentration. These results indicate that the origin of the incorporated hydrogen is attributed to the residual water vapor in the coating chamber, and that the variation of ρ and transmittance along with PH2O of the films resulted from the change in the grain size. On the contrary, the hydrogen concentration in H2/Ar-films was almost constant irrespective of PH2O and the degree of change in the grain size of the films versus PH2O was much smaller than that of Ar-films. These facts indicate that the hydrogen primarily comes from H2 gas and the adsorption species due to H2 gas preferentially adsorb to the growing film surface over residual water vapor. Consequently, the effects of PH2O on the crystal growth are reduced