Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 18: Rastersondentechniken II
O 18.3: Vortrag
Dienstag, 25. März 2003, 11:45–12:00, M\"UL/ELCH
A detailed study of photo-assisted tunneling spectroscopy and its application to polycristalline CIS solar cell surfaces — •U. Herber1, C. Heske1, E. Umbach1, F. Karg2 und T. Niesen2 — 1Experimentelle Physik II, Universität Würzburg, 97074 Würzburg — 2Shell Solar GmbH, München
Illuminating semiconductor samples with modulated light induces changes of band bending at the surface, giving rise to a photo-induced tunneling current (PITC). Such PITCs can be measured locally by scanning tunneling spectroscopy. However, every modulated process in scanning probe microscopies is accompanied by stray effects. In particular, an additional capacitance between sample and tip has to be taken into account when measuring local and modulated tunneling currents. By recording the modulated signal with a lock-in amplifier the phase difference of the complex current contributions can be determined. Hence, the tunneling fraction and the stray effects can be separated. The validity of this procedure is demonstrated and applied to Cu(In,Ga)Se2 thin film solar cell absorbers. This polycrystalline system reveals lateral inhomogeneities in both, phase and current amplitude. The findings will be discussed in view of different Schottky capacities in the subsurface region.