Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 12: Poster I
HL 12.5: Poster
Montag, 8. März 2004, 16:30–19:00, Poster A
Stray current contributions in photo-assisted tunneling spectroscopy on CIGSe absorbers: an aid or a nuisance? — •U. Herber1, C. Heske1, E. Umbach1, F. Karg2, T. P. Niesen2, G. Hanna3, and U. Rau3 — 1Experimentelle Physik II, Universität Würzburg, 97074 Würzburg — 2Shell Solar, München — 3Institut für Physikalische Elektronik, Universität Stuttgart, 70569 Stuttgart
Polycrystalline Cu(In,Ga)Se2 solar cell absorbers are investigated with photo-modulated scanning tunneling spectroscopy. For RTP (rapid thermal processing) absorbers, we find pronounced lateral inhomogeneities of the photo-induced tunneling current (PITC), as reported earlier [1]. In addition, similar inhomogeneities are also found on co-evaporated CIGSe absorbers.
However, every modulated process in scanning probe microscopies is accompanied by stray effects, in particular by an additional current contribution via the capacitance between sample and tip. The complex phase and amplitude of this stray signal can be measured separately, and thus its contribution can be subtracted from the PITC scan data. On the other hand, the stray signal is strongly determined by the (chemical) condition of the surface. The situation within a series of sputter-and-heat cycles is compared with corresponding photo-emission data and interpreted in the framework of the equivalent circuit approach.
[1] D. Eich et al., Thin Solid Films 361, 258 (2000)