Injected carrier distribution in a pentacene field effect transistor probed using optical second harmonic generation

The injected carrier distribution in a pentacene field effect transistor (FET) was examined using optical second harmonic generation (SHG) measurements. Results showed that the SHG signal representing the profile of carriers injected from the source electrode distributed along the channel depends on the biasing conditions. The enhanced SHG around the drain electrode under the biasing condition u[=(Vgs−Vth)/Vds]<1 was discussed based on the formation of an exhausted region of the distributed injected carriers. Organic FET (OFET) analysis, as a system of the Maxwell–Wagner (MW) effect element, suggests that injected carriers that are distributed along the pentacene-SiO2 interface in the region between x=0 (source electrode) and x=uL (L: channel length) decrease the SHG intensity in this region. The SHG experiments with MW analysis described herein are helpful in understanding the performance of the OFET channel region.