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

Abstract

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, Weinheim