Evolution and Recovery of Electrical Property of Reactive Sputtered Al-Doped ZnO Transparent Electrode Exposed to Harsh Environment

摘要

Al-doped ZnO (AZO) thin film is extensively studied as a promising alternative forSn-doped In_2O_3 (ITO) transparent electrode from the viewpoint of safety,environment, and material costs. However, most of AZO thin films are reportedto degrade when exposed to high humidity. To find a key factor of durability, theelectrical properties of AZO thin films after harsh conditions are characterizedin this study. AZO thin films are prepared on glass substrates by reactiveradiofrequency magnetron sputtering, followed by annealing at 400–550℃ in ahydrogen atmosphere. For harsh environment, a damp heat test is performed at85℃ and 85% relative humidity, where the changes in both the carrier concentrationand mobility are examined. It is found that the carrier concentrationexhibits similar decreasing tendencies to conductivity degradation as a functionof annealing temperature. This means that higher temperature contributes to thestability of carrier concentration, i.e., conductivity. Re-annealing is also conductedfor the AZO samples after the damp heat test, and the original conductivity issuccessfully recovered. This indicates that the degradation mechanism involvesthe chemical aspect rather than physical damage such as cracks, which cannot berecovered by annealing.