Oxygen vacancies and hydrogen in amorphous In-Ga-Zn-O and ZnO

Abstract

Hydrogen is known to be present as an impurity in amorphous oxide semiconductors at the 0.1% level. The behavior of hydrogen and oxygen vacancies in amorphous In-Ga-Zn-O is studied using density functional supercell calculations. We show that the hydrogens pair up at oxygen vacancies in the amorphous network, where they form metal-H-metal bridge bonds. These bonds are shown to create filled defect gap states lying just above the valence band edge, infra-red modes at about 1400 and 1520 cm-1 , and they are shown to give a consistent mechanism to explain the negative bias illumination stress instability found in oxide semiconductors like In-Ga-Zn-O (IGZO).

The Nature of the Oxygen Vacancy in Amorphous Oxide Semiconductors: Shallow Versus Deep

“…For other cases, the deep level always develops at weak bonding between metal atoms involving at least one In atom. Consistently, in previous calculations that analyzed the bonding environments around V O , it was revealed that the defect formation energy is lower when V O is surrounded by In atoms. Among the five models, defect levels are scattered over 1.7–2.1 eV from CBM.…”

“…However, the conclusion on the nature of V O is sharply divided; while V O was found to be dominantly deep in Refs. , shallow property was also claimed in Refs. .…”

“…Because of experimental difficulty in isolating the property of point defects, the density functional theory (DFT) calculations have been useful in investigating V O in a ‐IGZO . However, the conclusion on the nature of V O is sharply divided; while V O was found to be dominantly deep in Refs.…”

“…We also note that the small band gap may unduly favor shallow‐type donors by discounting the energy cost for generating defect levels close to the conduction band. Indeed, hybrid functional calculations producing a large band‐gap (>3 eV) favored deep states compared to (semi)local functionals …”

Role of the third metal oxide in In–Ga–Zn–O4 amorphous oxide semiconductors: Alternatives to gallium

“…Zn in ZnO has the d 10 s 0 electronic structure so that it also retains its high mobility in the amorphous (a-) phase. However ZnO is not easily made amorphous, with amorphisation of ZnO costing 0.4 eV per formula unit [15]. A second conductive oxide should be added to the ZnO to reduce the amorphization energy to be less than 0.15 eV/atom by the mixed alkali effect [15].…”