Comparative Study on Physical Properties of ZnO:Al Thin Films by in Situ Hydrogen Doping and Hydrogen Plasma Post-Treatment

Abstract

ZnO:Al (AZO) thin films were prepared on glass substrates by radio frequency magnetron sputtering at 300℃. Effects of H_2/(H_2 + Ar) flow rate ratio (R_H) during sputtering and post-deposition hydrogen plasma treatment on structural, electrical, and optical properties of AZO thin films were investigated and compared. For the films deposited with different R_H, all the films exhibited a (002) preferred orientation only along the c-axis and their 2θ angles decreased with increasing R_H. The lowest resistivity was obtained for the samples sputtered with R_H of 2%. The average optical transmittance in the visible wavelength region (400~700 nm) was over 85% and it slightly increased with increasing R_H. For the hydrogen plasmatreated films, the 2θ position of the (0 0 2) peak shifted to high angle side. The electrical resistivities of the hydrogen plasma-treated AZO (R_H =0) and AZO:H (R_H =2%) thin films decreased by 78% and 32%, respectively, compared to those without plasma treatment. It reveals that the hydrogen plasma treatment improves the conductivity of the non-hydrogen-doped AZO film more effectively than the hydrogen-doped one. Besides, hydrogen plasma treatment nearly did not change the optical transmittance in the visible wavelength region but broadened the optical bandgap of the film. These results suggest that the postdeposition hydrogen plasma treatment is more effective than in situ hydrogen doping in improving electrooptical properties of the AZO thin films.