Intrinsic nature of visible-light absorption in amorphous semiconducting oxides

To enlighten microscopic origin of visible-light absorption in transparent amorphous semiconducting oxides, the intrinsic optical property of amorphous InGaZnO4 is investigated by considering dipole transitions within the quasiparticle band structure. In comparison with the crystalline InGaZnO 4 with the optical gap of 3.6 eV, the amorphous InGaZnO4 has two distinct features developed in the band structure that contribute to significant visible-light absorption. First, the conduction bands are down-shifted by 0.55 eV mainly due to the undercoordinated In atoms, reducing the optical gap between extended states to 2.8 eV. Second, tail states formed by localized oxygen p orbitals are distributed over ∼0.5 eV near the valence edge, which give rise to substantial subgap absorption. The fundamental understanding on the optical property of amorphous semiconducting oxides based on underlying electronic structure will pave the way for resolving instability issues in recent display devices incorporating the semiconducting oxides. © 2014 Author(s).1881sciescopu

Source of instability at the amorphous interface between InGaZnO4 and SiO2: A theoretical investigation

In order to identify the source of charge trapping sites causing the device instability, we carry out ab initio calculations on the interface between amorphous SiO2 and InGaZnO4. The interface structure is modeled by joining the two amorphous phases with additional annealing steps. The theoretical band offset is obtained by aligning oxygen 2s levels and shows good agreement with experiment. For the stoichiometric interface, we could not identify any defects within the gap that can capture positive holes. However, when oxygen vacancies are introduced at the interface, the Si-metal bonds are formed, resulting in the defect levels within the band gap. When positively charged with holes, the Si-metal bonds undergo huge relaxations, implying that the recovery to the original neutral state should involve a large energy barrier. Such oxygen vacancies at the interface may play as charge-trapping sites, affecting the long-term device instability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim1441sciescopu