Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes

Hulea, I. N.; Russo, Saverio; Molinari, Anna; Morpurgo, Alberto F.

doi:10.1063/1.2185632

Cited by 54 publications

(46 citation statements)

References 15 publications

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“…These criteria, although plausible, have never been thoroughly investigated. Our recent and unexpected finding of the record-low contact resistance in devices with nickel electrodes ͑100 ⍀ cm͒ 7 clearly underscores the importance to explore a broader class of materials.…”

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confidence: 99%

Bias-dependent contact resistance in rubrene single-crystal field-effect transistors

Molinari

Gutiérrez

Hulea

et al. 2007

Applied Physics Letters

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The authors report a systematic study of the bias-dependent contact resistance in rubrene single-crystal field-effect transistors with Ni, Co, Cu, Au, and Pt electrodes. They show that the reproducibility in the values of contact resistance strongly depends on the metal, ranging from a factor of 2 for Ni to more than three orders of magnitude for Au. Surprisingly, field-effect transistors with Ni, Co, and Cu contacts exhibit an unexpected reproducibility of the bias-dependent differential conductance of the contacts once this has been normalized to the value measured at zero bias. This reproducibility may enable the study of microscopic carrier injection processes into organic semiconductors. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2741411͔ Considerable improvements in the material control of organic thin films are now enabling the reproducible, lowcost fabrication of organic field-effect transistors ͑FETs͒ with mobility values in the range of 0.1-1 cm 2 /V s. 1 These values are sufficient for the development of applications in the field of plastic electronics. 2 However, the fabrication of highquality electrical contacts for organic transistors has not progressed comparably, 3 and contacts are now posing limits to the performance of organic FETs. Specifically, with mobility values in between 0.1 and 1 cm 2 / V s, the contact resistance-typically larger than 1 k⍀ cm even in the best devices-limits the transistor performance as soon as the channel length becomes smaller than Ӎ10 m, 4 preventing the possibility of device downscaling. Irreproducibility makes the situation even worse: for gold-contacted pentacene thin-film FETs, for instance, the spread in contact resistance values was recently observed to exceed three orders of magnitude ͑from 2 k⍀ cm to more than 1 M⍀ cm͒. 5 The current lack of understanding of the microscopic carrier injection 6 processes from a metal electrode into an organic semiconductor does not help us in determining the causes of the observed irreproducibility and more systematic experiments are needed.Here we report systematic transport measurements of rubrene ͑C 42 H 28 ͒ single-crystal FETs with electrodes made of five different metals ͑Ni, Co, Cu, Au, and Pt͒. All the transistors have been fabricated with a sufficiently short channel length, so that the total device resistance is entirely dominated by the contacts. By studying more than 250 contactdominated devices, we have collected enough statistics to determine the average contact resistance, its spread in values, as well as its bias dependence. We find significant differences between the different metals. In particular, for nickel-which exhibits the lowest resistance-the spread is only a factor of 2, for cobalt and copper slightly more than one order of magnitude, and for gold more than three orders of magnitude ͑platinum seems to behave similarly to gold, but the number of devices tested was not sufficient to make more quantitative statements͒. We also find that for Ni, Cu, and Co ͑but nor for Au and Pt͒ the bias depe...

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confidence: 99%

Bias-dependent contact resistance in rubrene single-crystal field-effect transistors

Molinari

Gutiérrez

Hulea

et al. 2007

Applied Physics Letters

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“…7 As the quality of molecular crystals increases, transport of charge carriers across the interfaces between metal electrodes and the organic material starts to determine the performance of the devices. 13 Metal organic interfaces (MOIs) often give rise to a non-Ohmic behavior, indicating the existence of significant Schottky barriers.…”

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First-principles study of the dipole layer formation at metal-organic interfaces

et al. 2010

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We study the dipole layer formed at metal-organic interfaces by means of first-principles calculations. Interface dipoles are monitored by calculating the work function change of Au, Ag, Al, Mg and Ca surfaces upon adsorption of a monolayer of PTCDA (3,4,9,10-perylene-tetra-carboxylic-dianhydride), perylene or benzene molecules. Adsorption of PTCDA leads to pinning of the work function for a range of metal substrates. It gives interface dipoles that compensate for the difference in the clean metal work functions, leading to a nearly constant work function. In contrast, adsorption of benzene always results in a decrease of the work function, which is relatively constant for all metal substrates. Both effects are found in perylene, where adsorption on low work function metals gives work function pinning, whereas adsorption on high work function metals gives work function lowering. The work function changes upon adsorption are analyzed and interpreted in terms of two competing effects. If the molecule and substrate interact weakly, the molecule pushes electrons into the surface, which lowers the work function. If the metal work function is sufficiently low with respect to the unoccupied states of the molecule, electrons are donated into these states, which increases the binding and the work function.

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“…1,2 They can serve as light-sensing optoelectronic devices termed phototransistors (OPTs), if the semiconductor comprising the active channel is photosensitive. 3 In recent years, research on OPTs has been active on bringing the best of organic materials, application-tuned functionality, to an increasing number of applications, e.g., lightinduced switches, 4 inverters, 5 memory circuits, 6 and highly sensitive image sensors.…”

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“…This value is close to 5 kX cm measured in bottom-gate/top-contact rubrene SC-FETs. 2 OPT performance is analysed based on three figures-ofmerit: light responsivity (R ph ), photosensitivity (P), and EQE. These parameters enable a normalized comparison between devices.…”

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Ultrasensitive organic phototransistors with multispectral response based on thin-film/single-crystal bilayer structures

Pinto

Gouveia

Neves

et al. 2015

Applied Physics Letters

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We report on highly efficient organic phototransistors (OPTs) based on thin-film/single-crystal planar bilayer junctions between 5,6,11,12-tetraphenyltetracene (rubrene) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The OPTs show good field-effect characteristics in the dark, with high hole-mobility (4–5 cm2 V−1 s−1), low-contact resistance (20 kΩ cm), and low-operating voltage (≤5 V). Excellent sensing capabilities allow for light detection in the 400–750 nm range, with photocurrent/dark current ratio as high as 4 × 104, responsivity on the order of 20 AW−1 at 27 μW cm−2, and an external quantum efficiency of 52 000%. Photocurrent generation is attributed to enhanced electron and hole transfer at the interface between rubrene and PC61BM, and fast response times are observed as a consequence of the high-mobility of the interfaces. The optoelectronic properties exhibited in these OPTs outperform those typically provided by a-Si based devices, enabling future applications where multifunctionality in a single-device is sought.

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Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes

Cited by 54 publications

References 15 publications

Bias-dependent contact resistance in rubrene single-crystal field-effect transistors

Bias-dependent contact resistance in rubrene single-crystal field-effect transistors

First-principles study of the dipole layer formation at metal-organic interfaces

Ultrasensitive organic phototransistors with multispectral response based on thin-film/single-crystal bilayer structures

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