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Electronic Structure of Oxygen Interstitial Defects in Amorphous In-Ga-Zn-O Semiconductors and Implications for Device Behavior

W. H. Han, Young Jun Oh, and K. J. Chang*

Ji-Sang Park

  • Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea

  • National Renewable Energy Laboratory, Golden, Colorado 80401, USA

  • *kjchang@kaist.ac.kr
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Phys. Rev. Applied 3, 044008 – Published 16 April, 2015

DOI: https://doi.org/10.1103/PhysRevApplied.3.044008

Abstract

We investigate the atomic and electronic properties of O interstitial defects in amorphous In-Ga-Zn-O (a-IGZO) through density-functional calculations. We find that an O interstitial forms a dimer with a host O atom in its neutral state, but the O—O dimer bond is easily broken upon electron capture. When bond-breaking relaxations take place, the antibonding defect level of the dimer is significantly lowered from the conduction band toward the valence-band edge, making it energetically more favorable for the dimer to capture two electrons. With the hybrid functional for the exchange-correlation energy, the agreement of the energy barrier for two-electron capture with an experiment is greatly improved. The implication of the results is that O interstitials act as electron traps for the Fermi level close to the conduction-band edge; thus, excess O atoms can be the origin of positive shifts of threshold voltage observed under positive-bias stress in a-IGZO thin-film transistors. On the other hand, under light-illumination or negative-bias stress, which lower the Fermi level to the valence-band edge, the original dimer configuration is recovered by capturing hole carriers without any energy barrier, and the stability of current-voltage characteristics is restored.

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Phys. Rev. Applied 3, 044008– Published 16 April, 2015
  • Received 10 February 2015

© 2015 American Physical Society

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