Charge transport in nanoscale vertical organic semiconductor pillar devices

Wilbers, Janine G. E.; Xu, Bojian; Bobbert, Peter A.; Jong, Machiel Pieter de; Wiel, Wilfred G. van der

doi:10.1038/srep41171

Cited by 11 publications

(11 citation statements)

References 58 publications

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“…Secondly, when decreasing the organic layer thickness, the current densityvoltage characteristics become more sensitive to the charge injection and collection processes at the electrode interfaces, which may not be described to a sufficient level of accuracy. The smaller temperature dependence of the current density for small device thicknesses might indicate that the role of longer-distance temperature-independent tunneling processes becomes more significant [44]. Nevertheless, we conclude from our analysis that Coulomb correlation can indeed have a significant effect on current density-voltage characteristics of thin sandwich-type devices.…”

Section: B Comparison With Experimentscontrasting

confidence: 46%

“…The injection barriers at both electrodes are taken equal, consistent with the analysis of the experimental data given in Ref. [44]. In the figure, we have included all available experimental data that were obtained for devices with the same circular surface area, with a diameter of 2 μm.…”

Section: B Comparison With Experimentsmentioning

confidence: 65%

“…To investigate the relevance of the Coulomb correlation in realistic devices, we use the simulation approach developed in this work to analyze the hole-only current density-voltage characteristics of ultrathin sandwich-type devices with regioregular poly(3-hexylthiophene) (P3HT) layers in between gold electrodes measured recently by Wilbers et al [44]. The authors demonstrated that by spin-coating P3HT layers on a gold bottom electrode, followed by gently contacting a patterned gold top electrode using a wedging transfer technique, devices can be fabricated reliably with P3HT layer thicknesses down to 5 nm.…”

Section: B Comparison With Experimentsmentioning

confidence: 99%

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Effect of Coulomb correlation on charge transport in disordered organic semiconductors

Liu

Eersel²,

et al. 2017

Phys. Rev. B

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Charge transport in disordered organic semiconductors, which is governed by incoherent hopping between localized molecular states, is frequently studied using a mean-field approach. However, such an approach only considers the time-averaged occupation of sites and neglects the correlation effect resulting from the Coulomb interaction between charge carriers. Here, we study the charge transport in unipolar organic devices using kinetic Monte Carlo simulations and show that the effect of Coulomb correlation is already important when the charge-carrier concentration is above 10 −3 per molecular site and the electric field is smaller than 10 8 V/m. The mean-field approach is then no longer valid, and neglecting the effect can result in significant errors in device modeling. This finding is supported by experimental current density-voltage characteristics of ultrathin sandwich-type unipolar poly(3-hexylthiophene) (P3HT) devices, where high carrier concentrations are reached.

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Section: B Comparison With Experimentscontrasting

confidence: 46%

Section: B Comparison With Experimentsmentioning

confidence: 65%

Section: B Comparison With Experimentsmentioning

confidence: 99%

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Effect of Coulomb correlation on charge transport in disordered organic semiconductors

Liu

Eersel²,

et al. 2017

Phys. Rev. B

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“…

requires a large transistor width and a short transistor channel length in order to excel in the mentioned attributes. [11,12] However, when the channel length of an OFET approaches the 100 nm regime, high electric fields result in large bulk current densities that cannot be modulated efficiently via a gate-field. Yet for planar OFETs, the device area increases with the width and decreasing the channel length demands high-resolution patterning.

…”

mentioning

confidence: 99%

Short‐Channel Vertical Organic Field‐Effect Transistors with High On/Off Ratios

Doǧan

Verbeek

Kronemeijer

et al. 2019

Adv Elect Materials

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requires a large transistor width and a short transistor channel length in order to excel in the mentioned attributes. [7][8][9][10] From the architectural perspective, in an integrated pixelated device, transistors should also have small footprints so that light-emitting/-sensing devices can occupy larger areas on each pixel. Yet for planar OFETs, the device area increases with the width and decreasing the channel length demands high-resolution patterning. A vertical geometry allows reduced area requirements by employing a submicrometer thick organic film as the transistor channel. [11,12] However, when the channel length of an OFET approaches the 100 nm regime, high electric fields result in large bulk current densities that cannot be modulated efficiently via a gate-field. [13][14][15] This phenomenon is known as the shortchannel effect and it restricts further improvement of vertical OFETs (VOFETs).In this report, a novel VOFET geometry is demonstrated addressing the short-channel effect, in particular by suppressing the undesired bulk current. It is based on a gate electrode consisting of massively parallel highly doped silicon nanopillars (Figure 1). Crucially different from other VOFETs, an insulating layer is deposited on top of the bottom contact in order to force injection of the charge carriers only from the sides of the bottom metal, and current flow within a thin layer close to the gate dielectric, minimizing space-charge limited current through the bulk semiconductor. Thanks to this unique geometry, ON/OFF ratios up to 10 6 can be realized, i.e., at least three orders of magnitude larger than in previously reported short-channel (100 nm) VOFETs. [11,15] In order to fabricate the nanopillars with a high areal density (≈10 6 pillars mm −2 ), optical resist dots (100 nm radius) arranged in a hexagonal lattice (250 nm lattice constant) are created using displacement Talbot lithography (DTL). It allows for fast wafer-scale patterning. [16] This resist dot pattern acts as an etch mask during etching of about 300 nm into the underlying silicon. Since the silicon is highly doped p-type (resistivity of 0.010-0.025 Ω cm), it can be directly used as a massively parallel nanopillar gate electrode for a single device (≈7 × 10 5 pillars per device of total size 0.7 µm 2 ). In our experiments, we use bulk silicon wafers, but silicon-on-insulator wafers can be used in order to electrically separate individual many-pillar devices. A stoichiometric low-pressure chemical-vapor-deposited (LPCVD) 45 nm silicon nitride (Si 3 N 4 ) isolates these A unique vertical organic field-effect transistor structure in which highly doped silicon nanopillars are utilized as a gate electrode is demonstrated. An additional dielectric layer, partly covering the source, suppresses bulk conduction and lowers the OFF current. Using a semiconducting polymer as active channel material, short-channel (100 nm) transistors with ON/OFF current ratios up to 10 6 are realized. The electronic behavior is explained using space-charge and contact-lim...

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“…On the other hand, nanostructured emitters, with relevant aspect ratio, have high field enhancement factor, that is a high local electric field, favoring field emission under a very low macroscopic field. For these reasons, in recent years, the field emission properties of several nanostructures (nanoparticles, [21,22] pillars, [23,24] nanowires, [25,26] nanotubes, [27][28][29] and 2D layers [30][31][32] ) have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Field Emission Characteristics of InSb Patterned Nanowires

Giubileo¹,

Passacantando

Urban

et al. 2020

Adv Elect Materials

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properties toward next-generation electronic, optoelectronic, and photovoltaic devices, [1,5-8] such as field-effect-transistors, [9-11] and infrared detectors. [12,13] For instance, high mobility up to 77 000 cm 2 V −1 s −1 have been reported in InSb NWbased field-effect-transistors. [9] The use of InSb NWs to realize IR detectors working from mid-to long wavelength region has been reported. [14,15] Mid-infrared photodetectors based on a metal-semiconductormetal structure have been fabricated using electrochemically synthesized InSb NWs, showing high stability and excellent responsivity (8.4 × 10 4 AW −1). [15] Such enhanced properties have been explained in terms of high surface-to-volume ratio and 1D nanostructure of the photodetectors that significantly reduce the scattering and trapping phenomena, as well as the transit time between the electrodes. Multispectral optical absorptance in the short and mid-IR regions has been demonstrated [12] in top-down etched InSb NWs arrays, obtained by reactive ion etching of thin films produced by molecular beam epitaxy. In particular, it is possible to obtain highly tunable absorptance from 1.61 to 6.86 µm. [12] Furthermore, InSb NWs with diameter below 50 nm reach the quantum capacitance limit, providing significant improvement in device performance. [16] Single crystalline n-type InSb NWs have also been demonstrated as gas sensors at room temperature for NO 2 detection down to one part-per-million. [17] InSb NWs are promising candidates also for developing large area cold cathodes. It has been reported that the electron tunneling barrier is reduced due to high carrier concentration and relevant surface accumulation layer in InSb NWs. [18] This InSb nanowire arrays with different geometrical parameters, diameter and pitch, are fabricated by a top-down etching process on Si(100) substrates. Field emission properties of InSb nanowires are investigated by using a nano-manipulated tip anode inside of a scanning electron microscope. Stable field emission current is reported, with a maximum intensity extracted from a single nanowire of 1 µA, corresponding to a current density as high as 10 4 A cm −2. Stability and robustness of the nanowire is probed by monitoring field emission current for about 3 h. By tuning the cathode-anode distance in the range 500-1300 nm, the field enhancement factor and the turn-on field exhibit non-monotonic dependence, with maximum enhancement β ≈ 78 and minimum turn-on field E ON ≈ 0.033 V nm −1 for a separation d = 900 nm. The reduction of pitch between nanowires and the increase of diameter cause the reduction of the field emission performance, with reduced field enhancement (β < 60) and increased turn-on field (E ON ≈ 0.050 V nm −1). Finally, finite element simulation of the electric field distribution in the system demonstrates that emission is limited to an effective area near the border of the nanowire top surface, with annular shape and maximum width of 10 nm.

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Charge transport in nanoscale vertical organic semiconductor pillar devices

Cited by 11 publications

References 58 publications

Effect of Coulomb correlation on charge transport in disordered organic semiconductors

Effect of Coulomb correlation on charge transport in disordered organic semiconductors

Short‐Channel Vertical Organic Field‐Effect Transistors with High On/Off Ratios

Field Emission Characteristics of InSb Patterned Nanowires

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