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 ( E 0 ) 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 ∼10 19 cm –3 , Hall mobilities larger than 10 cm 2 (V s) –1 were obtained for the high‐quality films, while they were only several cm 2 (V s) –1 for low‐quality films that have large E 0 values ∼20 meV. However, even for low‐quality films, the E 0 value decreased from 20 meV to 7 meV and their Hall mobilities were increased from ∼1 cm 2 to >10 cm 2 (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)