| 1. |
- Charrier, D. S. H., et al.
(författare)
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Bimolecular recombination in ambipolar organic field effect transistors
- 2009
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 10:5, s. 994-997
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Tidskriftsartikel (refereegranskat)abstract
- In ambipolar organic field effect transistors (OFET) the shape of the channel potential is intimately related to the recombination zone width W, and hence to the electron-hole recombination strength. Experimentally, the recombination profile can be assessed by scanning Kelvin probe microscopy (SKPM). However, surface potentials as measured by SKPM are distorted due to spurious capacitive couplings. Here, we present a (de)convolution method with an experimentally calibrated transfer function to reconstruct the actual surface potential from a measured SKPM response and vice versa. Using this scheme, we find W = 0.5 mu m for a nickel dithiolene OFET, which translates into a recombination rate that is two orders of magnitude below the value expected for Langevin recombination. (C) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Gallego-Sala, Angela V., et al.
(författare)
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Latitudinal limits to the predicted increase of the peatland carbon sink with warming
- 2018
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Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
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Tidskriftsartikel (refereegranskat)abstract
- The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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| 3. |
- Roelofs, W. S. C., et al.
(författare)
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Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole-terthiophene)
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 98:20
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Tidskriftsartikel (refereegranskat)abstract
- Ambipolar integrated circuits were prepared with poly (diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm(2)/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3589986]
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| 4. |
- Kemerink, M., et al.
(författare)
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On the width of the recombination zone in ambipolar organic field effect transistors
- 2008
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- The performance of organic light emitting field effect transistors is strongly influenced by the width of the recombination zone. We present an analytical model for the recombination profile. By assuming Langevin recombination, the recombination zone width W is found to be given by W = root 4.34d delta, with d and delta the gate dielectric and accumulation layer thicknesses, respectively. The model compares favorably to both numerical calculations and measured surface potential profiles of an actual ambipolar device. (C) 2008 American Institute of Physics.
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| 5. |
- Mathijssen, S. G. J., et al.
(författare)
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Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress
- 2007
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 90:19
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Tidskriftsartikel (refereegranskat)abstract
- The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current. (C) 2007 American Institute of Physics.
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| 6. |
- Roelofs, W. S. C., et al.
(författare)
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Accurate description of charge transport in organic field effect transistors using an experimentally extracted density of states
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:8
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Tidskriftsartikel (refereegranskat)abstract
- The width and shape of the density of states (DOS) are key parameters to describe the charge transport of organic semiconductors. Here we extract the DOS using scanning Kelvin probe microscopy on a self-assembled monolayer field effect transistor (SAMFET). The semiconductor is only a single monolayer which has allowed extraction of the DOS over a wide energy range, pushing the methodology to its fundamental limit. The measured DOS consists of an exponential distribution of deep states with additional localized states on top. The charge transport has been calculated in a generic variable range-hopping model that allows any DOS as input. We show that with the experimentally extracted DOS an excellent agreement between measured and calculated transfer curves is obtained. This shows that detailed knowledge of the density of states is a prerequisite to consistently describe the transfer characteristics of organic field effect transistors.
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| 7. |
- Christian Roelofs, W. S., et al.
(författare)
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Fundamental Limitations for Electroluminescence in Organic Dual-Gate Field-Effect Transistors
- 2014
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 26:26, s. 4450-
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Tidskriftsartikel (refereegranskat)abstract
- A dual-gate organic field-effect transistor is investigated for electrically pumped lasing. The two gates can independently accumulate electrons and holes, yielding current densities exceeding the lasing threshold. Here, the aim is to force the electrons and holes to recombine by confining the charges in a single semiconducting film. It is found that independent hole and electron accumulation is mutually exclusive with vertical recombination and light emission.
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| 8. |
- Sharma, A., et al.
(författare)
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Anomalous current transients in organic field-effect transistors
- 2010
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 96:10
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Tidskriftsartikel (refereegranskat)abstract
- Here we study the origin of the gate bias-stress effect in organic p-type transistors. Based on water-mediated exchange between holes in the semiconductor and protons in the gate dielectric, we predict anomalous current transients for a non-constant gate bias, while ensuring accumulation. When applying a strongly negative gate bias followed by a less negative bias a back-transfer of protons to holes and an increase of the current is expected. We verify this counterintuitive behavior experimentally and can quantitatively model the transients with the same parameters as used to describe the threshold voltage shift. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3339879]
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| 9. |
- Sharma, A., et al.
(författare)
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Effect of Coulomb scattering from trapped charges on the mobility in an organic field-effect transistor
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of Coulomb scattering from trapped charges on the mobility in the two-dimensional channel of an organic field-effect transistor. The number of trapped charges can be tuned by applying a prolonged gate bias. Surprisingly, after increasing the number of trapped charges to a level where strong Coulomb scattering is expected, the mobility has decreased only slightly. Simulations show that this can be explained by assuming that the trapped charges are located in the gate dielectric at a significant distance from the channel instead of in or very close to the channel. The effect of Coulomb scattering is then strongly reduced.
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| 10. |
- Sharma, A., et al.
(författare)
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Proton migration mechanism for operational instabilities in organic field-effect transistors
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:7
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Tidskriftsartikel (refereegranskat)abstract
- Organic field-effect transistors exhibit operational instabilities involving a shift of the threshold gate voltage when a gate bias is applied. For a constant gate bias the threshold voltage shifts toward the applied gate bias voltage, an effect known as the bias-stress effect. Here, we report on a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric both for a constant as well as for a dynamic gate bias. We associate the instabilities with a reversible reaction in the organic semiconductor in which holes are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we show how a shorter period of application of a gate bias leads to a faster backward shift of the threshold voltage when the gate bias is removed. The proposed mechanism is consistent with the observed acceleration of the bias-stress effect with increasing humidity, increasing temperature, and increasing energy of the highest molecular orbital of the organic semiconductor.
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