Al-doped ZnO (AZO) thin film is extensively studied as a promising alternative for Sn-doped In 2 O 3 (ITO) transparent electrode from the viewpoint of safety, environment, and material costs. However, most of AZO thin films are reported to degrade when exposed to high humidity. To find a key factor of durability, the electrical properties of AZO thin films after harsh conditions are characterized in this study. AZO thin films are prepared on glass substrates by reactive radiofrequency magnetron sputtering, followed by annealing at 400-550 C in a hydrogen atmosphere. For harsh environment, a damp heat test is performed at 85 C and 85% relative humidity, where the changes in both the carrier concentration and mobility are examined. It is found that the carrier concentration exhibits similar decreasing tendencies to conductivity degradation as a function of annealing temperature. This means that higher temperature contributes to the stability of carrier concentration, i.e., conductivity. Re-annealing is also conducted for the AZO samples after the damp heat test, and the original conductivity is successfully recovered. This indicates that the degradation mechanism involves the chemical aspect rather than physical damage such as cracks, which cannot be recovered by annealing.
Al-doped ZnO (AZO) transparent electrodes deposited by reactive sputtering are investigated to clarify the influences of crystal orientations on film durability. During the deposition, argon gas flow was varied from 3 to 60 sccm amidst fixed oxygen gas flow at 60 sccm. With increasing argon gas flow, the crystal orientations exhibit a major transition from ( 110) to (002). During damp heat test at 85% relative humidity and 85°C, the films with more variations in crystal orientations exhibit more decreased Hall mobility, while the films having crystal orientation (002) exhibit less reduced carrier concentrations. Conductivity degradation over time is monotonous with argon gas flow, and the tendency is more similar to reduced carrier concentrations rather than decreased mobility. It is suggested that the degradation differences among AZO films are rather caused by the effectiveness of major crystal orientation in protecting carrier concentrations.
Fe2V0.9W0.1Al thin films are prepared on n-type Si substrates by means of radio-frequency magnetron sputtering with varied substrate temperatures from 743 – 1043 K, then subsequently annealed for one hour in vacuum at 1043 K. The thin films deposited at 1043 K are chemically degraded, exhibiting a low Seebeck coefficient, –65 µVK–1, at 330 K. On the other hand, the films deposited at 943 K possess –100 µVK–1 in Seebeck coefficient at around 330 – 350 K, which is very similar to the Seebeck coefficient of the bulk W-substituted Fe2VAl that possesses well-ordered L21 structure. The maximum power factor of 1.6 mWm–1K–2 was obtained for the sample deposited at 943 K. Accordingly, with the thermal conductivity of 3.5 Wm-1K-1, the figure of merit reached up to ZT = 0.16, which is comparable with Fe2V0.9W0.1Al of bulks and two times larger than that of the thin films of Si-substituted Fe2VAl.
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