Effects of hydrogen on the optical and electrical characteristics of the sputter-deposited Al₂O₃-doped ZnO thin films

In this study, AZO thin films were deposited on glass by using a 98 mol% ZnO + 1 mol% Al₂O₃ (AZO, Zn: Al = 98: 2) ceramic target and a r.f. magnetron sputtering system. At first, the effects of different H₂ flow rates (H₂/(H₂ + Ar) = 0%9.09%, abbreviated as H₂-deposited AZO thin films, deposition temperature was 200°C) added during the deposition process on the physical and electrical properties of AZO thin films were investigated. The optical transmittance at 400 nm700 nm is more than 80% for all AZO thin films regardless of H₂ flow rate and the transparency ratio decreased as the H ₂ flow rate increased. The Burstein-Moss shift effect was used to prove that the defects of AZO thin films decreased with increasing H₂ flow rate. Also, the 2% H₂-deposited AZO thin films were also treated by the H₂ plasma at room temperature for 60 min (plasma-treated AZO thin films). The value variations in the optical band gap (E g) values of the H₂-deposited and plasma-treated AZO thin films were evaluated from the plots of h 2 = c (h - E g), and the E g values increased with increasing H₂ flow rate. The E g values also increased as the H₂-plasma process was used to treat on the H₂-deposited Al₂O₃-doped ZnO (AZO) thin films.