Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 52: Organic semiconductors II

HL 52.4: Talk

Friday, March 27, 2009, 11:00–11:15, POT 51

The influence of field- and density- dependent mobility and contact properties on OFETs — •Susanne Scheinert¹ and Gernot Paasch² — ¹TU Ilmenau, Germany — ²IFW Dresden, Germany

The current characteristics of organic field-effect transistors (OFET) show often a disadvantageous non-linearity at low drain voltages. We have already proved (J. Appl. Phys. 102, 054509 (2007)) that in top contact OFETs this effect can be caused by trap recharging, if the contacts are of Schottky type. For bottom contact OFETs, in spite of controversial discussions, the effect is repeatedly attributed to Schottky contacts. We show that such non-linearity does occur in bottom contact OFETs only in the special case with a Schottky contact with large ideality factor as drain and an Ohmic contact at source. However, if the dependence of the mobility on carrier concentration and field is taken into account, Schottky contacts at both source and drain can cause the non-linearity. The effect has been investigated by numerical 2D-simulations incorporating for the mobility the field dependent Pool/Frenkel model and two models, which in addition depend on the carrier concentration, the Limketai model and the Pasveer/Coehoorn model. Analysis of the simulated profiles of concentrations and fields allows us to clarify the mechanism causing the non-linearity, which is particularly effective for the Pasveer/Coehoorn model. Based on the achieved understanding of the mechanism, we discuss strategies to prevent the non-linearity.