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HL: Fachverband Halbleiterphysik
HL 92: Poster Session: Structure and transport in organic photovoltaics; Photovoltaics; Impurities/Amorphous semiconductors; New materials
HL 92.17: Poster
Thursday, March 14, 2013, 16:00–20:00, Poster A
Analysis of electronic subgap states in amorphous semiconductor oxides on the example of Zn-Sn-O — Wolfgang Körner1, •Daniel F. Urban1, and Christian Elsässer1,2 — 1Fraunhofer Institute for Mechanics of Materials IWM, Freiburg — 2IAM-ZBS, Karlsruhe Institute of Technology
A molecular dynamics and density-functional-theory study of amorphous Zn-Sn-O with focus on the use as transparent conducting oxide material is presented. The amorphous structures generated by MD are subsequently relaxed using the local-density-approximation of DFT. The Zn/Sn ratio, the oxygen content and individual point defects are investigated concerning their thermodynamic and electronic properties and compared to the data for crystalline structures. Defect levels in the electronic band structure of ZnO are analyzed in terms of the density of states, which is calculated within the LDA and with a self-interaction-correction. We relate the electronic sub-gap states, which were recently observed experimentally, to structural features of the amorphous samples. We find the valence band tail, caused by the disordered O 2p orbitals, to be superimposed by deep defect states that can be assigned to under-coordinated O atoms. Doping with H atoms is found to suppress these states and improves the transparency. The deep levels below the conduction band arise mainly from under-coordinated Sn atoms or Zn--Sn pairs. The addition of oxygen can be a possible route to reduce such defect levels.[2]
[1] W. Körner, P. Gumbsch and C. Elsässer, PRB (2012) accepted.
[2] W. Körner and C. Elsässer, Thin Solid Films (2012) submitted.