Regensburg 2007 – wissenschaftliches Programm
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 8: Poster Session SYOE
SYOE 8.82: Poster
Dienstag, 27. März 2007, 18:00–20:00, Poster B
Bipolaron Mechanism for Hysteresis in Organic Field-Effect Devices — •Gernot Paasch1 and Susanne Scheinert2 — 1IFW Dresden, Germany — 2TU Ilmenau, Germany
Hysteresis effects occur usually in organic field-effect transistors or MOS capacitors. The capacitance-voltage curves for the two sweep directions of the gate voltage differ essentially by different flat band voltages, or equivalently different interface charges. In contrast to statements in the literature, trap recharging does not lead to this type of hysteresis [1]. We show that formation and dissociation of bipolarons (BP) or polaron pairs (PP) can cause this hysteresis in MOS capacitors with conjugated polymers as organic semiconductor. For energetically favored BPs (PPs) sufficient amount of the accumulation charge can be transformed into BPs (PPs) during the sweep from depletion to accumulation and the subsequent waiting time. At the beginning of the reverse sweep, the dissociation is retarded and the BPs (PPs) remain for some time at the interface leading to the shifted flat band voltage. For a quantitative estimate of the relevant relaxation times we made use of the reaction rate for BP formation determined recently from bias stress experiments [2].
[1] Th. Lindner, G. Paasch, S. Scheinert, J. Appl. Phys. 98, 114505 (2005).
[2] A. Salleo, R. A. Street, Phys. Rev. B 70, 235324 (2004).