Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures

Lezama, Ignacio Gutiérrez; Nakano, Masaki; Minder, Nikolas A.; Chen, Zhihua; Girolamo, F. V. Di; Facchetti, Antonio; Morpurgo, Alberto F.

doi:10.1038/nmat3383

Cited by 79 publications

(81 citation statements)

References 36 publications

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“…This can be observed in recent examples of crystal on crystal lamination. Conjugating tetramethyltetraselenafulvalene and TCNQ crystals, for instance, forms a small-gap semiconductor system 34 , whereas in PDIF-CN 2 (N,N 0 -1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide) and rubrene system the valence band of the electron donor (rubrene) and the conduction band of the electron acceptor (PDIF-CN 2 ) are practically aligned 35 . As a result, the interfacial electron density presents a linear dependence of the temperature.…”

Section: Resultsmentioning

confidence: 99%

Photoconductive response in organic charge transfer interfaces with high quantum efficiency

2013

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Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1 A W À 1 , corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications.

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Section: Resultsmentioning

confidence: 99%

Photoconductive response in organic charge transfer interfaces with high quantum efficiency

2013

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“…[1][2][3][4][5][6][7] For these devices, a junction with a large energy barrier provides rectifi cation, leading to a diode behavior, whereas a relatively small energy barrier provides a highly conductive nonrectifying behavior, resulting in efficient carrier injection into (or extraction from) the molecular semiconductor. [ 4 ] Typically, a specifi c metal/molecular semiconductor combination leads to a fi xed energy barrier, which crucially determines the device performance and effi ciency; [8][9][10] therefore, the possibility of a gate-controlled energy barrier is very appealing from the point of view of possible advanced applications.…”

Section: Introductionmentioning

confidence: 99%

Gate‐Controlled Energy Barrier at a Graphene/Molecular Semiconductor Junction

Parui

Pietrobon

Ciudad

et al. 2015

Adv Funct Materials

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wileyonlinelibrary.comGraphene, [ 11 ] a one-atom thick zero band gap semiconductor has allowed the development of new electronic device schemes such as the graphene-barristor, [ 12 ] the graphene-vertical-fi eld-effecttransistor (VFET), [13][14][15][16] and the graphenebase hot electron transistor. [ 17 ] In organic electronics, graphene can be an ideal choice to use as the injector (or source) electrode for a VFET since its Fermi level, its corresponding work function and its available low density of states (DOS) [ 18 ] can all be easily modulated, providing a tunable energy barrier which eventually controls the device operation. In addition, the electric fi eld produced by a gate electrode will extend into the organic semiconductor, as the monolayer thickness of graphene is insuffi cient to fully screen it. [ 13,19 ] In order to increase the performance of organic thin fi lm transistors (OTFT) compared with the inorganic counterparts, a unique vertical architecture with a molecular semiconductor (C 60 ) was fi rst demonstrated using a thin and rough (with a roughness comparable to the thickness) metal electrode. [ 20 ] A clear advantage of the vertical over the lateral organic transistor geometry is that the channel length is controlled by the thickness of the organic layer and the devices can be downsized in both the lateral and the vertical directions. In the case of a perforated metallic source electrode, the electric fi eld can directly access the metal/organic interface which causes the energy level realignment (similar to the band bending in inorganic semiconductor) in the organic semiconductor. Although Ma and Yang have reported a large on/off current ratio (≈10 6 ), the high DOS and the fi xed work function of the metallic electrode (injector) limits its application to a few organic semiconductors. [ 20 ] Later on, Liu et al. introduced a carbon nanotube-based source electrode with low DOS in organic VFETs for a wide range of organic semiconductors. [ 21 ] Carbon nanotubes allow new mechanisms for transistor operation such as the tuning of the gate modulated energy barrier. Graphene, similar to carbon nanotubes in its electrical and mechanical properties, has additional advantages over them due to the large-scale availability (chemical vapor deposition (CVD)-grown graphene) of chemically inert high quality 2D surfaces. [ 14,22 ] On the other hand, fullerene (C 60 ) is one of the most widely studied molecular semiconductors [ 2,5,20,[23][24][25] and a common choice as an active media for transistors. C 60 has an energy gap ( E g = 1.7 eV), between its highest occupied molecular orbital Gate-Controlled Energy Barrier at a Graphene/Molecular Semiconductor JunctionSubir Parui , * Luca Pietrobon , David Ciudad , Saül Vélez , Xiangnan Sun , Fèlix Casanova , Pablo Stoliar , and Luis E. Hueso * The formation of an energy-barrier at a metal/molecular semiconductor junction is a universal phenomenon which limits the performance of many molecular semiconductor-based electronic devices, from fi eld-effect trans...

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“…To this end, Alves et al [38] and Gutierrez et al [39] showed that charge-transfer states formed at the interface of two bulk organic crystals could be exploited for device applications. We believe the concept developed here will be able to realize more versatile structures such as planar, vertical heterostructures and quantum wells.…”

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confidence: 99%

Probing Carrier Transport and Structure-Property Relationship of Highly Ordered Organic Semiconductors at the Two-Dimensional Limit

et al. 2016

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One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two-dimensionally in the first few molecular layers near the dielectric interface.Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered mono-to tetra-layer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to band-like in subsequent layers.Such abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ~3nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals. 3Organic field-effect transistors (OFETs) offer unique advantages of low cost, lightweight and flexibility and are widely used in electronics and display industry.While the mobility of bulk organic semiconductors has increased dramatically [1][2][3], an outstanding issue is to directly examine the structure-property relationship at the semiconductor-dielectric interface [4], where charge transport actually occurs [5][6][7].Ultrathin organic semiconductors down to few-nanometre thickness are often dominated by traps and disorders and far away from intrinsic transport regime [8][9][10].Another challenge in organic electronics is the development of layer-by-layer epitaxy with the precision similar to molecular beam epitaxy in their inorganic counterparts [11]. These challenges may be alleviated if molecular crystals are processed into large-area, highly crystalline monolayers. Such 2D form factor will also bring about new applications such as nanoporous membranes and insulating dielectrics [12,13].Several recent breakthroughs in various types of 2D organic materials such as polymers [14,15], oligomers [16] and covalent organic frameworks [17] have already shown great promises along this direction. However, one of the most fundamental questions regarding the nature of charge transport at the 2D limit has not been addressed. In this work, we study the benchmark molecule pentacene epitaxially crystallized on BN substrate because of its high mobility and simple structure to model. The highly clean system allows us to provide the first definitive scenario of how molecular packing and charge transport are modulated near the interface, without being dominated by extrinsic factors. Our results suggest the possibility of band-like transport...

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Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures

Cited by 79 publications

References 36 publications

Photoconductive response in organic charge transfer interfaces with high quantum efficiency

Photoconductive response in organic charge transfer interfaces with high quantum efficiency

Gate‐Controlled Energy Barrier at a Graphene/Molecular Semiconductor Junction

Probing Carrier Transport and Structure-Property Relationship of Highly Ordered Organic Semiconductors at the Two-Dimensional Limit

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