The Effect of Carbon Nanotube/Organic Semiconductor Interfacial Area on the Performance of Organic Transistors

We show that the performance of pentacene transistors can be significantly improved by maximizing the interfacial area at single walled carbon nanotube (SWCNT)/pentacene. The interfacial areas are varied by anchoring short SWCNTs of different densities (0-30/{\mu}m) to the Pd electrodes. The average mobility is increased three, six and nine times for low, medium and high SWCNT densities, respectively, compared to the devices with zero SWCNT. The current on-off ratio and on-current are increased up to 40 times and 20 times with increasing the SWCNT density. We explain the improved device performance using reduced barrier height of SWCNT/pentacene interface.Comment: 9 pages, 7 figures, 1 tabl

Semiconducting enriched carbon nanotube align arrays of tunable density and their electrical transport properties

We demonstrate assembly of solution processed semiconducting enriched (99%) single walled carbon nanotubes (s-SWNT) in an array with varying linear density via ac-dielectrophoresis and investigate detailed electronic transport properties of the fabricated devices. We show that (i) the quality of the alignment varies with frequency of the applied voltage and that (ii) by varying the frequency and concentration of the solution, we can control the linear density of the s-SWNTs in the array from 1/{\mu}m to 25 /{\mu}m. The maximum linear density of 25 s-SWNT /\mum reported here is the highest for any aligned semiconducting array. The DEP assembled s-SWNT devices provide opportunity to investigate transport property of the arrays in the direct transport regime. Room temperature electron transport measurements of the fabricated devices show that with increasing nanotube density the device mobility increases while the current on-off ratio decreases dramatically. For the dense array, the device current density was 16 {\mu}A/{\mu}m, on-conductance was 390 {\mu}S, and sheet resistance was 30 k{\Omega}/\square. These values are the best reported so far for any semiconducting nanotube array.Comment: 18 pages, 8 figures, 1 tabl

Position dependent photodetector from large area reduced graphene oxide thin films

We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets

Near-infrared photoresponse in single walled carbon nanotube/polymer composite films

We present a near-infrared photoresponse study of single-walled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (SWCNT/P3HT-b-PS) composite films for different loading ratios of SWCNT in the polymer matrix. Compared to the pure SWCNT film, the photoresponse [(light current - dark current)/dark current] is much larger in the SWCNT/polymer composite films. The photoresponse is up to 157% when SWCNTs are embedded in P3HT-b-PS while for a pure SWCNT film it is only 40%. We also show that the photocurrent strongly depends on the position of the laser spot with maximum photocurrent occurring at the metal-film interface. We explain the photoresponse due to exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode - SWCNT interfaceComment: CARBON (in press

Diffusion mediated photoconduction in multi-walled carbon nanotube films

We investigated the mechanism for photoconduction in multi-walled carbon nanotube (MWNT) film of various electrode separations upon near infrared illumination. In addition to observing strong dependence of photocurrent on the position of the laser spot, we found that the time constant of the dynamic photoresponse is slow and increases with increasing electrode separations. The photoconduction mechanism can be explained by the Schottky barrier modulation at the metal-nanotube film interface and charge carrier diffusion through percolating MWNT networks.Comment: 6 pages, 5 figure

High-performance short channel organic transistors using densely aligned carbon nanotube array electrodes

We report high-performance short channel pentacene field effect transistor (FET) using carbon nanotube aligned array electrodes. The devices show field effect mobility of up to 0.65 cm(2)/Vs and current on-off ratio of up to 1.7 x 10(6), which is the best for sub-micron pentacene FETs. The calculated cutoff frequency (f(c)) of the devices is up to 211 MHz which is among the best reported f(c) for organic transistors. The high performance of our short channel FET is attributed to improved charge injections from the aligned array carbon nanotube electrodes into the pentacene

Thermionic Emission And Tunneling At Carbon Nanotube-Organic Semiconductor Interface

Figure Persented: We study the charge carrier injection mechanism across the carbon nanotube (CNT)-organic semiconductor interface using a densely aligned carbon nanotube array as electrode and pentacene as organic semiconductor. The current density-voltage (J-V) characteristics measured at different temperatures show a transition from a thermal emission mechanism at high temperature (above 200 K) to a tunneling mechanism at low temperature (below 200 K). A barrier height of ∼0.16 eV is calculated from the thermal emission regime, which is much lower compared to the metal/pentacene devices. At low temperatures, the J-V curves exhibit a direct tunneling mechanism at low bias, corresponding to a trapezoidal barrier, while at high bias the mechanism is well described by Fowler-Nordheim tunneling, which corresponds to a triangular barrier. A transition from direct tunneling to Fowler-Nordheim tunneling further signifies a small injection barrier at the CNT/pentacene interface. Our results presented here are the first direct experimental evidence of low charge carrier injection barrier between CNT electrodes and an organic semiconductor and are a significant step forward in realizing the overall goal of using CNT electrodes in organic electronics. © 2012 American Chemical Society

Lower Activation Energy In Organic Field Effect Transistors With Carbon Nanotube Contacts

We study temperature dependent charge transport properties of pentacene field effect transistors (FET) with carbon nanotube (CNT) electrodes. The field effect mobilities at different temperatures and gate voltages follow activated hopping behavior from which we calculate an activation energy of 48 meV for the CNT contacted pentacene FET. This value is lower than that of our control Pd contacted pentacene FET device (83 meV). The lower activation energy of the CNT contacted devices is attributed to improved CNT/pentacene interface. © 2014 Elsevier Ltd. All rights reserved