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Injection Barriers (injection + barrier)

Distribution by Scientific Domains

Polymers and Materials Science	54%
Physics and Astronomy	36%

Selected Abstracts

Tunable Injection Barrier in Organic Resistive Switches Based on Phase-Separated Ferroelectric,Semiconductor Blends,

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Kamal Asadi
Abstract Organic non-volatile resistive bistable diodes based on phase-separated blends of ferroelectric and semiconducting polymers are fabricated. The polarization field of the ferroelectric modulates the injection barrier at the semiconductor,electrode contact and, hence, the resistance of the comprising diodes. Comparison between the on- and off-current of the switching diodes, with the current measured for semiconductor-only diodes reveals that the switching occurs between bulk-limited, i.e., space-charge-limited, and injection-limited current transport. By deliberately varying the HOMO energy of the semiconductor and the work-function of the metal electrode, it is demonstrated that injection barriers up to 1.6,eV can be surmounted by the ferroelectric polarization yielding on/off current modulations of more than five orders of magnitude. The exponential dependence of the current modulation with a slope of 0.25,eV/decade is rationalized by the magnitude of the injection barrier. [source]

Enhanced Performance of Fullerene n-Channel Field-Effect Transistors with Titanium Sub-Oxide Injection Layer

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Shinuk Cho
Abstract Enhanced performance of n-channel organic field-effect transistors (OFETs) is demonstrated by introducing a titanium sub-oxide (TiOx) injection layer. The n-channel OFETs utilize [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) as the semiconductor in the channel. With the TiOx injection layer, the electron mobilities of PC61BM and PC71BM FET using Al as source/drain electrodes are comparable to those obtained from OFETs using Ca as the source/drain electrodes. Direct measurement of contact resistance (Rc) shows significantly decreased Rc values for FETs with the TiOx layer. Ultraviolet photoelectron spectroscopy (UPS) studies demonstrate that the TiOx layer reduces the electron injection barrier because of the relatively strong interfacial dipole of TiOx. In addition to functioning as an electron injection layer that eliminates the contact resistance, the TiOx layer acts as a passivation layer that prevents penetration of O2 and H2O; devices with the TiOx injection layer exhibit a significant improvement in lifetime when exposed to air. [source]

Effect of Traps on Carrier Injection and Transport in Organic Field-effect Transistor

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010
Martin Weis Non-member
Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Potentiometry on pentacene OFETs: Charge carrier mobilities and injection barriers in bottom and top contact configurations

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008
R. Scholz
Abstract In a combination of experimental techniques including electrical probes, potentiometry, and charge transient spectroscopy (QTS), we develop concepts how to quantify the potential drops at the contacts, the mobility in the channel region, and the density of states of deep traps in pentacene OFETs. For OFETs grown from unpurified pentacene on pre-patterned Au bottom contacts, a comparison between potentiometry and two-dimensional device simulations determines an injection barrier of 0.73 eV at the source contact and a hole mobility of 0.014 cm2 V,1 s,1 in the pentacene channel. Temperature-dependent QTS data reveal a trap level at about 125 meV from the hole transport band, indicating a relatively high density of unintentional dopants and therefore a high background density of majority charge carriers. In OFETs grown from purified pentacene onto a SiO2 gate dielectric and Au top contacts evaporated onto the pentacene channel without breaking the vacuum, potentiometry reveals a nearly perfect alignment of the metal work function with the hole transport level in the organic layer. The much lower density of deep traps in these samples raises the hole mobility to the range 0.1,0.2 cm2 V,1 s,1. A further improvement of the hole mobility and the resulting device performance can be achieved by a chemical treatment of the gate oxide with n-octadecytrichlorosilane (OTS). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Tunable Injection Barrier in Organic Resistive Switches Based on Phase-Separated Ferroelectric,Semiconductor Blends,

Influences of Connecting Unit Architecture on the Performance of Tandem Organic Light-Emitting Devices,

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007
Y. Chan
Abstract The present work investigates the influence of the n-type layer in the connecting unit on the performance of tandem organic light-emitting devices (OLEDs). The n-type layer is typically an organic electron-transporting layer doped with reactive metals. By systematically varying the metal dopants and the electron-transporting hosts, we have identified the important factors affecting the performance of the tandem OLEDs. Contrary to common belief, device characteristics were found to be insensitive to metal work functions, as supported by the ultraviolet photoemission spectroscopy results that the lowest unoccupied molecular orbitals of all metal-doped n-type layers studied here have similar energy levels. It suggests that the electron injection barriers from the connecting units are not sensitive to the metal dopant used. On the other hand, it was found that performance of the n-type layers depends on their electrical conductivities which can be improved by using an electron-transporting host with higher electron mobility. This effect is further modulated by the optical transparency of constituent organic layers. The efficiency of tandem OLEDs would decrease as the optical transmittance decreases. [source]

Investigation of Charge-Carrier Injection in Ambipolar Organic Light-Emitting Field-Effect Transistors

ADVANCED MATERIALS, Issue 10-11 2009
Martin Schidleja
Organic light-emitting field-effect transistors provide a deeper insight into the physics of ambipolar devices. Here, the source and drain contacts are altered to investigate the influence of injection barriers on the performance of ambipolar field-effect transistors. The experimental results are compared to a straightforward numerical model. [source]

Influence of charge carrier mobility on the performance of organic solar cells

PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 4 2008
Carsten Deibel
Abstract The power conversion efficiency of organic solar cells based on donor,acceptor blends is governed by an interplay of polaron pair dissociation and bimolecular polaron recombination. Both processes are strongly dependent on the charge carrier mobility, the dissociation increasing with faster charge transport, with raised recombination losses at the same time. Using a macroscopic effective medium simulation, we calculate the optimum charge carrier mobility for the highest power conversion efficiency, for the first time accounting for injection barriers and a reduced Langevin-type recombination. An enhancement of the charge carrier mobility from 10,8 m2/V s for state of the art polymer,fullerene solar cells to about 10,6 m2/V s, which yields the maximum efficiency, corresponds to an improvement of only about 20% for the given parameter set. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Potentiometry on pentacene OFETs: Charge carrier mobilities and injection barriers in bottom and top contact configurations

Alignment of the energy levels and charge injection barriers at interfaces for spin injection: La0.7Sr0.3MnO3 in contact with organic semiconductors

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
M. Grobosch
Abstract For determination of the energy-level alignment at inter- faces between La0.7Sr0.3MnO3 films and two typical organic semiconductors, copper-phthalocyanine (CuPc) and ,-sexithiophene (,-6T) we have performed a combined X-ray and ultraviolet photoemission study. La0.7Sr0.3MnO3 thin films were grown by using the pulsed laser deposition (PLD) technique and subsequently ex-situ cleaned before the organic materials were thermally evaporated. We show that under these conditions the interfaces are free from chemical interaction and are characterized by a short-range interface dipole and large injection barriers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]