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HL: Fachverband Halbleiterphysik

HL 99: Electronic structure theory

HL 99.8: Vortrag

Donnerstag, 3. April 2014, 16:45–17:00, POT 151

Origin of electronic subgap states in amorphous semiconductor oxides on the example of In-Ga-Zn-O (IGZO) — Wolfgang Körner, •Daniel Urban, and Christian Elsässer — Fraunhofer IWM, Freiburg, Germany

A density-functional-theory study of amorphous In-Ga-Zn-O (IGZO) with focus on the use as transparent conducting oxide is presented [1]. We studied stoichiometric and oxygen-poor amorphous IGZO samples concerning their electronic properties and compared the results to those for crystalline IGZO. Subgap states in the electronic density of states of amorphous IGZO due to imperfections are calculated by means of the LDA and with a self-interaction-correction (SIC). In our study we relate the electronic subgap states, which were observed recently by Nomura et al. [2] to structural features of the amorphous samples. According to our analysis the valence band tail, caused by the disordered O 2p orbitals, is superimposed by deep defect states above the valence band which can be assigned to undercoordinated O atoms. Our interpretation is further supported by the observation that additional H suppresses these states by creating O-H bonds. This hydrogen doping improves the transparency and is consistent with experimental findings [2]. The deep levels below the conduction band arise mainly from miscoordinated metal atoms, mostly In--Zn pairs. By addition of O, i.e., by oxygen annealing, the frequency of such defect levels can be reduced.

[1] W. Körner, D. F. Urban and C. Elsässer, J. Appl. Phys. 114, 163704 (2013). [2] K. Nomura et al., J. Appl.Phys. 109, 073726 (2011).