Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 3: Organic Devices I

SYSA 3.5: Vortrag

Dienstag, 26. Februar 2008, 15:45–16:00, H 2013

Observation of charge injection and trapping in depleted channels of organic field effect transistors — •Christopher Siol, Christian Melzer, and Heinz von Seggern — Electronic Materials Division, Institute of Materials Science, Technische Universität Darmstadt, Petersenstr. 23, 64287 Darmstadt, Germany

The measurement of I-V characteristics is the standard means of transistor investigation. However, it gives limited information about the electronic processes that determine the transistor operation. Kelvin probe force microscopy (KPFM), however, gives the opportunity to resolve the surface potential locally. This allows one to separate the injection phenomena from the charge transport in the channel.

Here the surface potential in the channel of n- and p-type pentacene OFETs with poly(methyl methacrylate) dielectrics has been measured during operation. In the on state the conducting accumulation layer links surface potential of the channels to the contact electrodes. However, driving the device into the off state causes depletion of the channel from mobile charge carriers. Then, the surface potential depends on the gate potential but might be altered due to the presence of trapped charges in the channel. Depending on the device history, such trapped charges are observed. Additionally, by applying high gate fields to the already depleted transistor an injection of complementary charge carriers has been observed even for high injection barriers.