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

Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of similar to 10 cm(2) V-1 s(-1) [K. Nomura , 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 In3+ 5s orbitals form an extended state with a band effective mass of similar to 0.2m(e) at the conduction band bottom.