Mechanism of conductivity degradation of AZO thin film in high humidity ambient

The conductivity stability of aluminum-doped zinc oxide (AZO) films was evaluated in the ambient with different humidity. We found that the conductivity of AZO films is sensitive to the humidity and degrades remarkably in high humidity ambient (90 ± 5% relative humidity) at 60 °C. Hall measurement results show that the conductivity degradation is due to the drop in the carrier concentration, while the carrier mobility is found to remain relatively constant in the high humidity ambient. XPS (X-ray photoelectron spectroscopy) analysis reveals that the oxygen-vacancies in the AZO thin films were greatly reduced in the high-humidity ambient. So, we believe that the high-humidity ambient causes the decrease in the oxygen vacancies and eventually resulted in the decrease in the concentration of the free carriers in the AZO thin films. In this study, a mechanism is proposed to explain the humidity-assist reduction in the oxygen vacancies in the humidity-tested AZO films. In addition, we report that the electrical properties of AZO film can be stabilized by coating a Cr layer on the AZO thin film surface.