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Origin of subgap states in amorphous In-Ga-Zn-O

: Körner, W.; Urban, D.F.; Elsässer, C.

Preprint urn:nbn:de:0011-n-2818197 (359 KByte PDF)
MD5 Fingerprint: 2d7e4c198b5a7b2bcfdfa1443e5aa6c9
Created on: 5.12.2014

Journal of applied physics 114 (2013), No.16, Art. 163704, 6 pp.
ISSN: 0021-8979
ISSN: 1089-7550
European Commission EC
FP7-NMP; 246334; ORAMA
Journal Article, Electronic Publication
Fraunhofer IWM ()
In-Ga-Zn-O (IGZO); amorph; transparent conductor oxide (TCO); amorphous semiconductor oxide (ASO); hydrogen doping; transparency

We present a density functional theory analysis of stoichiometric and nonstoichiometric, crystalline and amorphous In-Ga-Zn-O (c-IGZO, a-IGZO), which connects the recently experimentally discovered electronic subgap states to structural features of a-IGZO. In particular, we show that undercoordinated oxygen atoms create electronic defect levels in the lower half of the band gap up to about 1.5 eV above the valence band edge. As a second class of fundamental defects that appear in a-IGZO, we identify mainly pairs of metal atoms which are not separated by oxygen atoms in between. These defects cause electronic defect levels in the upper part of the band gap. Furthermore, we show that hydrogen doping can suppress the deep levels due to undercoordinated oxygen atoms while those of metal defects just undergo a shift within the band gap. Altogether our results provide an explanation for the experimentally observed effect that hydrogen doping increases the transparency and improves the conductivity of a-IGZO.