Surface Cu-depletion of Cu(In,Ga)Se2 thin films: Further experimental evidence for a defect-induced surface reconstruction

Journal of Applied Physics - Tập 107 Số 11 - 2010
Harry Mönig1,2, Ch.‐H. Fischer3,1, A. Grimm1, Benjamin Johnson1, Christian A. Kaufmann1, R. Caballero1, Iver Lauermann1, Martha Ch. Lux‐Steiner3,1
1Helmholtz-Zentrum Berlin für Materialien und Energie 1 , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
2Yale University 2 Center for Research on Interface Structure and Phenomena, , New Haven, Connecticut 06511, USA
3Freie Universität Berlin 3 Department of Physics, , 14195 Berlin, Germany

Tóm tắt

The surface Cu-depletion of chalcopyrite thin films and its influence on the interface properties of related solar cells have been subject of a controversial debate for many years. Although the nature of this Cu-depletion and its extension in depth are crucial for the device physics, there are only a few contradictory experimental results that address this topic. To clarify this issue, we performed depth-dependent compositional analysis by angle dependent soft x-ray emission spectroscopy (AXES) on Cu(In,Ga)Se2 thin films with different integral Cu-contents. By considering depth profiles from literature and by taking the accuracy of AXES into account, our numerical AXES simulations predict a pronounced angle dependence for our samples. However, our experimental data show only a minor angle dependence, which leads to the conclusion that the Cu-depleted surface layer must be restricted to a very thin surface layer, which is not accessible by AXES. This conclusion is consistent with the result from our previous investigation by hard x-ray photoelectron spectroscopy, where we found a Cu-depleted surface layer in the subnanometer regime. Consequently the present study gives further experimental evidence for the surface reconstruction model proposed by first-principles calculations. Supported by secondary neutral mass spectroscopy, we show that the minor angle dependence in our AXES data can be attributed to a Ga-gradient in the chalcopyrite material.

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Journal of Applied Physics

Tập 107 Số 11

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