Relationship between non‐localized tail states and carrier transport in amorphous oxide semiconductor, In–Ga–Zn–O

The relationship between non‐localized tail states and carrier transport in transparent amorphous oxide semiconductor, In–Ga–Zn–O (a‐IGZO), was investigated. It was found that the energy width (E0) of the non‐localized tail states varied from <7 meV to 20 meV depending on the film deposition conditions (i.e. film quality). At carrier concentrations of ∼1019 cm–3, Hall mobilities larger than 10 cm2 (V s)–1 were obtained for the high‐quality films, while they were only several cm2 (V s)–1 for low‐quality films that have large E0 values ∼20 meV. However, even for low‐quality films, the E0 value decreased from 20 meV to 7 meV and their Hall mobilities were increased from ∼1 cm2 to >10 cm2 (V s)–1 by post thermal annealing at ≥300 °C. These observations indicate that structural relaxation associated with electron transport starts from ∼300 °C, which is much lower than the crystallization temperature (∼520 °C). This situation is similar to the case of amorphous metals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)