ABSTRACTAmbipolar organic transistors are technologically interesting because of
their potential applications in light-emitting field-effect transistors [1]
and complementary-metal-oxide-semiconductor (CMOS) devices by providing ease
of design, low cost of fabrication, and flexibility [2]. Although common
organic semiconductors show either n- or p-type charge transport
characteristic, organic transistors with ambipolar characteristics have been
reported recently. In this work, we show that ambipolar transport can be
achieved within a single transistor channel using LiF gate dielectric in the
transistors with pentacene active layer. This ambipolar behavior can be
controlled by the applied source-drain and gate biases. It was found that at
low source-drain biases multistep hopping is the dominant conduction
mechanism, while in high voltage regimes I-V data fits in Fowler-Nordheim
(F-N) tunneling model. From the slope of the F-N plots, the dependency
between field enhancement factor and the transition point in conduction
mechanism upon gate bias has been extracted. The transition points show more
dependency on gate voltage for negative biases compared to the positive
biases. While sweeping negative gate voltages from -5 to -20 V, the
source-drain voltages change from about 27 to 17 V. On the other hand, for
positive gate voltages from 5 to 20 V, the value of the transition point
stays at approximately 36 V. In order to further understand the transport
mechanisms, new structures with an interface layer between dielectric and
active layer have been fabricated and characterized. As expected, a
significant decrease in the amount of the source-drain current has been
observed after introducing the interface layer.
Space Charge Transport Characteristic Considering the Non-Uniform Electric Effect of Ion Mobility