Analysis of carrier injection into a pentacene field effect transistor by optical second harmonic generation measurements

Optical second harmonic generation (SHG) measurements were used to clarify carrier injection into pentacene field effect transistors (FETs) with Au source and drain electrodes. The electric field was probed along the pentacene FET channel. Results showed that the SHG was enhanced depending on biasing voltages. In the off state of FET (V-gs >-30 V), the SHG was enhanced in proportion to the Laplace electric field formed in FET. On the other hand, in the on state (V-gs <-30 V), the enhanced SHG in the off state was diminished because of the hole injection from source electrode. Interestingly, in the off state of FET, electron injection from source and drain electrodes was also suggested. Furthermore, this electron injection was eliminated by overcoating the pentacene film by spin coating a polystyrene film. Finally, results show that our FET analysis based on a Maxwell-Wagner model is acceptable. (c) 2007 American Institute of Physics.