Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment andab initiocalculations

Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of 100. 3em{0ex}cm^20. 2em{0ex}V^-10. 2em{0ex}s^-1 K. Nomura et al. , Nature 488, 432 (2004). The local coordination structure in an IAOS, In-Ga-Zn-O (a-IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a-IGZO are similar to those in the corresponding crystalline phase, InGaZnO₄, and edge-sharing structures consisting of In-O polyhedra remain in the amorphous structure. The In^3+ 5s orbitals form an extended state with a band effective mass of 0. 2m₄ at the conduction band bottom.