Conference Presentation

PUBDB-2014-04031

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Chalcopyrite semiconductors: Atomic-scale structure and band gap bowing

Schnohr, C. (Corresponding Author)Extern* ; Eckner, S. ; Kämmer, H.Extern* ; Steinbach, T.Extern* ; Gnauck, M.Extern* ; Johannes, A.Extern* ; Kaufmann, C. A. ; Stephan, C.Extern* ; Schorr, S.Extern*

2014

Abstract: Cu(In,Ga)Se2 is one of the most promising material systems for thin film photovoltaics with record efficiencies above 20% on laboratory scale. The material crystallizes in the chalcopyrite type crystal structure where the anion is typically displaced from the ideal tetrahedral lattice site due to the different properties of the neighbouring cations. This subtle structural variation has a strong influence on the energy band gap. Therefore, we have studied the atomic-scale structure of Cu(In,Ga)Se2 as a function of composition using extended X-ray absorption fine structure spectroscopy and valence force field simulations [1]. The element-specific In-Se, Ga-Se and Cu-Se bond lengths are strikingly different from each other and remain close to the values of the ternary parent compounds despite the significant change of the lattice constants. The local atomic arrangements thus deviate significantly from the long-range crystallographic structure. Furthermore, the material is characterised by structural inhomogeneity on the atomic scale even if compositional fluctuations or secondary phases are absent. Regarding the anion position, two different displacement mechanisms have to be distinguished both of which influence the nonlinear change of the band gap with material composition. Similar results were also obtained for Cu(In,Ga)S2 indicating that our findings represent general features of these highly relevant yet complex chalcopyrite semiconductors [2]. [1] C. S. Schnohr, H. Kämmer, C. Stephan, S. Schorr, T. Steinbach, and J. Rensberg, Phys. Rev. B 85, 245204 (2012).[2] S. Eckner, H. Kämmer, T. Steinbach, M. Gnauck, A. Johannes, C. Stephan, S. Schorr, and C. S. Schnohr, Appl. Phys. Lett. 103, 081905 (2013).

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Contributing Institute(s):

1. DOOR-User (DOOR)

Research Program(s):

1. DORIS Beamline C (POF2-54G13) (POF2-54G13)
2. FS-Proposal: I-20110135 (I-20110135) (I-20110135)
3. FS-Proposal: I-20100027 (I-20100027) (I-20100027)

Experiment(s):

1. DORIS Beamline C (DORIS III)

Appears in the scientific report 2014

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