Hole trapping in polydiacetylene field effect transistor studied by optical second harmonic generation (original) (raw)
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Ieej Transactions on Fundamentals and Materials, 2007
To probe the carrier injection from Au source electrode into the channel of pentacene field effect transistors (FET), optical second harmonic generation (SHG) measurement is employed. SHG is enhanced at the off state due to Laplace electric field formation, whereas it is diminished at the on state. As the generation of SHG signal is in proportional to the electric field formed in the channel, we concluded that SHG measurement can probe the change of the electric field in the pentacene FET channel due to the injected and subsequently trapped holes.
Journal of Applied Physics, 2009
By probing optical second harmonic generation ͑SHG͒ signals enhanced around the injection electrode, the carrier injection mechanism of top-contact pentacene field-effect transistors ͑FETs͒ was investigated in terms of Schottky injection. At the Au source electrode, the SHG signal disappeared immediately after applying the driving voltage: the applied external electric field was cancelled by the space charge field formed by holes accumulated in the FET channel. At the Ag source electrode, the SH intensity decayed slowly. Its dependence on the device operation voltage suggested that the electric field was not relaxed by injected holes. The Schottky effect regulated carrier injection. The space charge field effect attributable to accumulated holes contributed to the carrier injection.
Probing of channel region in pentacene field effect transistor by optical second harmonic generation
Chemical Physics Letters, 2009
We studied the channel region at the gate insulator-active layer interface in pentacene field effect transistors (FETs) by using the electric field induced optical second harmonic generation (EFISHG) measurements. The SH signal was enhanced along the interface, dependent on biasing conditions, and reflected the region of accumulated holes that were injected from the source electrode. Analysing the charge accumulation condition along the channel, we explained the experimental EFISHG results.
Chemical Physics Letters, 2009
We studied the channel region at the gate insulator-active layer interface in pentacene field effect transistors (FETs) by using the electric field induced optical second harmonic generation (EFISHG) measurements. The SH signal was enhanced along the interface, dependent on biasing conditions, and reflected the region of accumulated holes that were injected from the source electrode. Analysing the charge accumulation condition along the channel, we explained the experimental EFISHG results.
Journal of Applied Physics, 2008
The injected carrier distribution in a pentacene field effect transistor ͑FET͒ was examined using optical second harmonic generation ͑SHG͒ 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 u͓=͑V gs − V th ͒ / V ds ͔ Ͻ 1 was discussed based on the formation of an exhausted region of the distributed injected carriers. Organic FET ͑OFET͒ analysis, as a system of the Maxwell-Wagner ͑MW͒ effect element, suggests that injected carriers that are distributed along the pentacene-SiO 2 interface in the region between x =0 ͑source electrode͒ and x = uL ͑L: channel length͒ 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.
Study of traps in polydiacetylene based devices using TSC technique
The European Physical Journal Applied Physics, 2006
Trap parameters in poly(1-(3,4-difluorophenyl)-2-(4-pentylcyclohexylphenyl)acetylene) (PDPA-2F) based devices have been investigated by using the thermally stimulated current (TSC) technique. The device structure is ITO-PEDOT-(PDPA-2F)-M, where M stands for the cathode metal (Al, Ca/Al, and Au). The results reveal at least three TSC peaks in devices denoted as peaks A, B and C. Comparing trap parameters in ITO-PEDOT-(PDPA-2F)-Au hole-only device and ITO-PEDOT-(PDPA-2F)-Ca Al (Al) bipolar devices, we assigned A and B trap types to hole-like traps and C type traps to electron-like traps. The trap densities are in the range of 10 15-10 17 cm −3 and the trap levels are 0.12 eV (A type traps), 0.36 eV (B type traps), and 0.25 eV (C type traps).
Thin Solid Films, 2008
a b s t r a c t Organic field-effect transistor SHG (optical second harmonic generation) Maxwell-Wagner effect Using electric field induced optical second harmonic generation (SHG) measurement, injected carrier distribution along the channel of pentacene field-effect transistor was examined, on focusing on the region around the drain electrode. The SH was enhanced depending on applied drain-source and gate-source voltages. It was suggested that the SH enhancement reflected the distribution and amount of holes accumulated at the pentacene-SiO 2 interface. Using the Maxwell-Wagner model analysis, carrier distribution along the channel was discussed in terms of the enhanced SH intensity profile.
Thin Solid Films, 2008
The pentacene field effect transistors (FETs)' operation for the injection carrier was revealed by means of the drain current-elapsed time (I ds-t) and optical second harmonic generation (SHG) measurements. The charge carriers forming the conducting channel of pentacene FETs were mainly holes injected from the Au source electrode. Carrier injection from source and drain electrodes was followed by the carrier trapping, and the SHG signal modulated by the change in the electric field distribution between Au the source and drain electrodes was shown. In particular, at the off state of the FET, electron injection and succeeding trapping were suggested. Furthermore, hole injection assisted by trapped electrons was also suggested.
Journal of Applied Physics, 2010
A significant difference between the transient electric field profiles of the pentacene organic field-effect transistors ͑OFETs͒ with SiO 2 and poly͑methyl-methacrylate͒ ͑PMMA͒ insulators was found by the time-resolved microscopic optical second-harmonic generation ͑TRM-SHG͒ experiment. The profile of former device was broad and changed smoothly, while the latter one had a sharp peak. Particularly, the peak of the transient electric field in SiO 2-insulated devices moved much faster than that in the PMMA-insulated one. Based on several experimental evidences and computational simulations, we proposed that these differences might arise from a higher trapped carrier density in the conductive channel on the PMMA insulator. Simple approaches were developed to evaluate the trap density and define dynamic carrier mobility in terms of the transient electric field measured by the TRM-SHG technique. This mobility quantitatively depicts that the transient hole transport in the OFET with the PMMA insulator is trap controlled.
Origin of electric field distribution in organic field-effect transistor: Experiment and analysis
Journal of Applied Physics, 2009
Electric field distribution in the pentacene organic field-effect transistor ͑OFET͒ channel is investigated using the microscopic optical second-harmonic generation ͑SHG͒. At the on-and off-states of the OFET, enhanced SHG signal was observed near the drain electrode and at the source and drain electrodes. Our analytical analysis indicates that the Laplace field formation is in the off-state of the OFET. The electric field profile in the on-state representing distribution by the space-charge formation in the channel due to injected carriers was calculated by the transmission line model. Theoretical models are confirmed by the experimental results and the result shows that pentacene can be used as a dielectric material. On the basis of estimated potential distribution in the on-state, a model for the evaluation of the drain-source current is proposed.