Physical properties of TiO2-doped zinc oxide thin films: Influence of plasma treatment in H2 and/or Ar gas ambient

Transparent conducting TiO2-doped zinc oxide (ZnO:Ti, TZO) thin films were prepared by radio-frequency magnetron sputtering and followed by plasma treatments with different H2/(H2 + Ar) flow ratio (RH2). The electrical, structural, and optical properties of the TZO thin films were investigated. Experimental results showed that resistivities of all the TZO thin films decreased after plasma treatment regardless of ambient gas, and the lowest resistivity was 1.13 × 10−3 Ω-cm (or 62% reduction) for RH2 = 50%. All the TZO thin films exhibited a (002) preferred orientation along the c-axis, indicating a typical wurtzite structure. Surface roughness of the TZO films slightly increased from 1.58 nm to 1.63-2.75 nm (RMS value) after plasma treatments. Average optical transmittance of the TZO films (containing glass substrates) in the visible region (400-700 nm) did not considerably change after plasma treatments and ranged from 82.7% to 84.3%. The largest figure of merit (FOM), 5.02 × 10−3 Ω−1, was achieved for the plasma-treated film with RH2 = 50%, and it increased by 237% as compared with that of the as-deposited film. These results indicate that the H2 + Ar (1:1) plasma treatment is more effective than pure H2 or Ar plasma treatment in improving opto-electronic properties of transparent conducting TZO thin films.