Dresden 2014 – wissenschaftliches Programm

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MI: Fachverband Mikrosonden

MI 8: Poster: Microanalysis and Microscopy

MI 8.4: Poster

Mittwoch, 2. April 2014, 17:00–19:30, P4

Determination of trap and band states in organic field-effect transistors by scanning Kelvin probe microscopy — •Sebastian Hietzschold^1,2, Michael Scherer^2,3, Janusz Schinke^2,3, Robert Lovrincic^2,3, and Wolfgang Kowalsky^2,3 — ¹Kirchhoff-Institut für Physik, Universität Heidelberg, Germany — ²InnovationLab, Heidelberg, Germany — ³Institut für Hochfrequenztechnik, Technische Universität Braunschweig, Germany

We determine the density of states (DOS) including gap states in organic semiconductors by means of scanning Kelvin probe microscopy (SKPM). We apply this energy resolving technique with high spatial resolution to bottom gate organic field-effect transistors (OFETs) using the small molecule organic semiconductor pentacene on either HMDS modified or unmodified silicon dioxide gate dielectric. Biasing the gate electrode leads to a filling and emptying of electronic states in the semiconductor resulting in a shift of the surface potential. Hereby we indirectly gain the density of trap as well as band states. The measurements were performed in both ambient atmosphere and ultra-high vacuum. Additionally we compare the results to transistors made of Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) which is widely used as an air stable solution processable organic p-type semiconductor. The DOS of PTAA exhibits several additional peaks compared to pentacene, probably related to impurity induced energy levels and a higher degree of structural disorder. Finally, we correlate the obtained DOS distributions to the device performances.