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1.
2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post‐silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering for these materials to create high‐performance devices while adapting for large‐area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS2 devices, for which a graphene film synthesized by chemical vapor deposition (CVD) is inserted between a CVD‐grown MoS2 film and a Ag electrode as an interfacial layer. The MoS2 field‐effect transistors with graphene/Ag contacts show improved electrical and photoelectrical properties, achieving a field‐effect mobility of 35 cm2 V?1 s?1, an on/off current ratio of 4 × 108, and a photoresponsivity of 2160 A W?1, compared to those of devices with conventional Ti/Au contacts. These improvements are attributed to the low work function of Ag and the tunability of graphene Fermi level; the n‐doping of Ag in graphene decreases its Fermi level, thereby reducing the Schottky barrier height and contact resistance between the MoS2 and electrodes. This demonstration of contact interface engineering with CVD‐grown MoS2 and graphene is a key step toward the practical application of atomically thin TMDC‐based devices with low‐resistance contacts for high‐performance large‐area electronics and optoelectronics.  相似文献   

2.

WSe2 is thought to be one of the best emerging p-type transition metal dichalcogenide (TMD) materials for potential low-power complementary metal oxide semiconductor (CMOS) circuit applications. However, the contact barrier and the interface quality hinder the performance of p-type field effect transistors (FETs) with WSe2 films. In this work, metals with different work functions—Pd, Pt, and Ag—were systematically investigated as contacts for WSe2 to decrease the contact resistances at source/drain electrodes and potentially improve transistor performance. Optimized p-type multilayer WSe2 FETs with Pd contacts were successfully fabricated, and excellent electrical characteristics were obtained: a hole mobility of 36 cm2V?1 s?1; a high on/off ratio, over 106; and a record low sub-threshold swing, SS?=?95 mV/dec, which may be attributed to the small Schottky barrier height of 295 meV between Pd and WSe2, and strong Fermi-level pinning near the top of the valence band at the interface. Finally, a full-functional CMOS inverter was also demonstrated, consisting of a p-type WSe2 FET together with a normal n-type MoS2 FET. This confirmed the potential of TMD FETs in future low-power CMOS digital circuit applications.

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3.
2D semiconductors are promising channel materials for field‐effect transistors (FETs) with potentially strong immunity to short‐channel effects (SCEs). In this paper, a grain boundary widening technique is developed to fabricate graphene electrodes for contacting monolayer MoS2. FETs with channel lengths scaling down to ≈4 nm can be realized reliably. These graphene‐contacted ultrashort channel MoS2 FETs exhibit superior performances including the nearly Ohmic contacts and excellent immunity to SCEs. This work provides a facile route toward the fabrication of various 2D material‐based devices for ultrascaled electronics.  相似文献   

4.
In recent past, for next‐generation device opportunities such as sub‐10 nm channel field‐effect transistors (FETs), tunneling FETs, and high‐end display backplanes, tremendous research on multilayered molybdenum disulfide (MoS2) among transition metal dichalcogenides has been actively performed. However, nonavailability on a matured threshold voltage control scheme, like a substitutional doping in Si technology, has been plagued for the prosperity of 2D materials in electronics. Herein, an adjustment scheme for threshold voltage of MoS2 FETs by using self‐assembled monolayer treatment via octadecyltrichlorosilane is proposed and demonstrated to show MoS2 FETs in an enhancement mode with preservation of electrical parameters such as field‐effect mobility, subthreshold swing, and current on–off ratio. Furthermore, the mechanisms for threshold voltage adjustment are systematically studied by using atomic force microscopy, Raman, temperature‐dependent electrical characterization, etc. For validation of effects of threshold voltage engineering on MoS2 FETs, full swing inverters, comprising enhancement mode drivers and depletion mode loads are perfectly demonstrated with a maximum gain of 18.2 and a noise margin of ≈45% of 1/2 VDD. More impressively, quantum dot light‐emitting diodes, driven by enhancement mode MoS2 FETs, stably demonstrate 120 cd m?2 at the gate‐to‐source voltage of 5 V, exhibiting promising opportunities for future display application.  相似文献   

5.
2D materials hold great potential for designing novel electronic and optoelectronic devices. However, 2D material can only absorb limited incident light. As a representative 2D semiconductor, monolayer MoS2 can only absorb up to 10% of the incident light in the visible, which is not sufficient to achieve a high optical‐to‐electrical conversion efficiency. To overcome this shortcoming, a “gap‐mode” plasmon‐enhanced monolayer MoS2 fluorescent emitter and photodetector is designed by squeezing the light‐field into Ag shell‐isolated nanoparticles–Au film gap, where the confined electromagnetic field can interact with monolayer MoS2. With this gap‐mode plasmon‐enhanced configuration, a 110‐fold enhancement of photoluminescence intensity is achieved, exceeding values reached by other plasmon‐enhanced MoS2 fluorescent emitters. In addition, a gap‐mode plasmon‐enhanced monolayer MoS2 photodetector with an 880% enhancement in photocurrent and a responsivity of 287.5 A W?1 is demonstrated, exceeding previously reported plasmon‐enhanced monolayer MoS2 photodetectors.  相似文献   

6.
The development of transition metal dichalcogenides has greatly accelerated research in the 2D realm, especially for layered MoS2. Crucially, the metallic MoS2 monolayer is an ideal platform in which novel topological electronic states can emerge and also exhibits excellent energy conversion and storage properties. However, as its intrinsic metallic phase, little is known about the nature of 2D 1T′‐MoS2, probably because of limited phase uniformity (<80%) and lateral size (usually <1 µm) in produced materials. Herein, solution processing to realize high phase‐purity 1T′‐MoS2 monolayers with large lateral size is demonstrated. Direct chemical exfoliation of millimeter‐sized 1T′ crystal is introduced to successfully produce a high‐yield of 1T′‐MoS2 monolayers with over 97% phase purity and unprecedentedly large size up to tens of micrometers. Furthermore, the large‐sized and high‐quality 1T′‐MoS2 nanosheets exhibit clear intrinsic superconductivity among all thicknesses down to monolayer, accompanied by a slow drop of transition temperature from 6.1 to 3.0 K. Prominently, unconventional superconducting behavior with upper critical field far beyond the Pauli limit is observed in the centrosymmetric 1T′‐MoS2 structure. The results open up an ideal approach to explore the properties of 2D metastable polymorphic materials.  相似文献   

7.
Doping of bulk silicon and III–V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS2 is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS2 lattice stems from the development of a new growth technology called dual‐additive chemical vapor deposition. First, the addition of a MnO2 additive to the MoS2 growth process reshapes the morphology and increases lateral size of Mn‐doped MoS2. Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS2 shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS2 electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS2 and potentially many other 2D materials to modify their properties.  相似文献   

8.
A facile methodology for the large‐scale production of layer‐controlled MoS2 layers on an inexpensive substrate involving a simple coating of single source precursor with subsequent roll‐to‐roll‐based thermal decomposition is developed. The resulting 50 cm long MoS2 layers synthesized on Ni foils possess excellent long‐range uniformity and optimum stoichiometry. Moreover, this methodology is promising because it enables simple control of the number of MoS2 layers by simply adjusting the concentration of (NH4)2MoS4. Additionally, the capability of the MoS2 for practical applications in electronic/optoelectronic devices and catalysts for hydrogen evolution reaction is verified. The MoS2‐based field effect transistors exhibit unipolar n‐channel transistor behavior with electron mobility of 0.6 cm2 V?1 s?1 and an on‐off ratio of ≈10³. The MoS2‐based visible‐light photodetectors are fabricated in order to evaluate their photoelectrical properties, obtaining an 100% yield for active devices with significant photocurrents and extracted photoresponsivity of ≈22 mA W?1. Moreover, the MoS2 layers on Ni foils exhibit applicable catalytic activity with observed overpotential of ≈165 mV and a Tafel slope of 133 mV dec?1. Based on these results, it is envisaged that the cost‐effective methodology will trigger actual industrial applications, as well as novel research related to 2D semiconductor‐based multifaceted applications.  相似文献   

9.
The minimization of the subthreshold swing (SS) in transistors is essential for low‐voltage operation and lower power consumption, both critical for mobile devices and internet of things (IoT) devices. The conventional metal‐oxide‐semiconductor field‐effect transistor requires sophisticated dielectric engineering to achieve nearly ideal SS (60 mV dec?1 at room temperature). However, another type of transistor, the junction field‐effect transistor (JFET) is free of dielectric layer and can reach the theoretical SS limit without complicated dielectric engineering. The construction of a 2D SnSe/MoS2 van der Waals (vdW) heterostructure‐based JFET with nearly ideal SS is reported. It is shown that the SnSe/MoS2 vdW heterostructure exhibits excellent p–n diode rectifying characteristics with low saturate current. Using the SnSe as the gate and MoS2 as the channel, the SnSe/MoS2 vdW heterostructure exhibit well‐behavioured n‐channel JFET characteristics with a small pinch‐off voltage VP of ?0.25 V, nearly ideal subthreshold swing SS of 60.3 mV dec?1 and high ON/OFF ratio over 106, demonstrating excellent electronic performance especially in the subthreshold regime.  相似文献   

10.
High‐quality and large‐area molybdenum disulfide (MoS2) thin film is highly desirable for applications in large‐area electronics. However, there remains a challenge in attaining MoS2 film of reasonable crystallinity due to the absence of appropriate choice and control of precursors, as well as choice of suitable growth substrates. Herein, a novel and facile route is reported for synthesizing few‐layered MoS2 film with new precursors via chemical vapor deposition. Prior to growth, an aqueous solution of sodium molybdate as the molybdenum precursor is spun onto the growth substrate and dimethyl disulfide as the liquid sulfur precursor is supplied with a bubbling system during growth. To supplement the limiting effect of Mo (sodium molybdate), a supplementary Mo is supplied by dissolving molybdenum hexacarbonyl (Mo(CO)6) in the liquid sulfur precursor delivered by the bubbler. By precisely controlling the amounts of precursors and hydrogen flow, full coverage of MoS2 film is readily achievable in 20 min. Large‐area MoS2 field effect transistors (FETs) fabricated with a conventional photolithography have a carrier mobility as high as 18.9 cm2 V?1 s?1, which is the highest reported for bottom‐gated MoS2‐FETs fabricated via photolithography with an on/off ratio of ≈105 at room temperature.  相似文献   

11.
Band‐like transport behavior of H‐doped transition metal dichalcogenide (TMD) channels in field effect transistors (FET) is studied by conducting low‐temperature electrical measurements, where MoTe2, WSe2, and MoS2 are chosen for channels. Doped with H atoms through atomic layer deposition, those channels show strong n‐type conduction and their mobility increases without losing on‐state current as the measurement temperature decreases. In contrast, the mobility of unintentionally (naturally) doped TMD FETs always drops at low temperatures whether they are p‐ or n‐type. Density functional theory calculations show that H‐doped MoTe2, WSe2, and MoS2 have Fermi levels above conduction band edge. It is thus concluded that the charge transport behavior in H‐doped TMD channels is metallic showing band‐like transport rather than thermal hopping. These results indicate that H‐doped TMD FETs are practically useful even at low‐temperature ranges.  相似文献   

12.
Due to the intriguing optical and electronic properties, 2D materials have attracted a lot of interest for the electronic and optoelectronic applications. Identifying new promising 2D materials will be rewarding toward the development of next generation 2D electronics. Here, palladium diselenide (PdSe2), a noble‐transition metal dichalcogenide (TMDC), is introduced as a promising high mobility 2D material into the fast growing 2D community. Field‐effect transistors (FETs) based on ultrathin PdSe2 show intrinsic ambipolar characteristic. The polarity of the FET can be tuned. After vacuum annealing, the authors find PdSe2 to exhibit electron‐dominated transport with high mobility (µ e (max) = 216 cm2 V?1 s?1) and on/off ratio up to 103. Hole‐dominated‐transport PdSe2 can be obtained by molecular doping using F4‐TCNQ. This pioneer work on PdSe2 will spark interests in the less explored regime of noble‐TMDCs.  相似文献   

13.
Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al2O3 layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (VD_SAT ≈ 3 V), change in VD_SAT with a gate voltage of only 0.12 V V?1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.  相似文献   

14.
MoS2 shows promising applications in photocatalytic water splitting, owing to its uniquely optical and electric properties. However, the insufficient light absorption and lack of performance stability are two crucial issues for efficient application of MoS2 nanomaterials. Here, Au nanoparticles (NPs)@MoS2 sub‐micrometer sphere‐ZnO nanorod (Au NPs@MoS2‐ZnO) hybrid photocatalysts have been successfully synthesized by a facile process combining the hydrothermal method and seed‐growth method. Such photocatalysts exhibit high efficiency and excellent stability for hydrogen production via multiple optical‐electrical effects. The introduction of Au NPs to MoS2 sub‐micrometer spheres forming a core–shell structure demonstrates strong plasmonic absorption enhancement and facilitates exciton separation. The incorporation of ZnO nanorods to the Au NPs@MoS2 hybrids further extends the light absorption to a broader wavelength region and enhances the exciton dissociation. In addition, mutual contacts between Au NPs (or ZnO nanorods) and the MoS2 spheres effectively protect the MoS2 nanosheets from peeling off from the spheres. More importantly, efficiently multiple exciton separations help to restrain the MoS2 nanomaterials from photocorrosion. As a result, the Au@MoS2‐ZnO hybrid structures exhibit an excellent hydrogen gas evolution (3737.4 μmol g?1) with improved stability (91.9% of activity remaining) after a long‐time test (32 h), which is one of the highest photocatalytic activities to date among the MoS2 based photocatalysts.  相似文献   

15.
Molybdenum disulfide (MoS2), a typical 2D metal dichalcogenide (2DMD), has exhibited tremendous potential in optoelectronic device applications, especially in photodetection. However, due to the weak light absorption of planar mono‐/multilayers, limited cutoff wavelength edge, and lack of high‐quality junctions, most reported MoS2‐based photodetectors show undesirable performance. Here, a structurized 3D heterojunction of RGO–MoS2/pyramid Si is demonstrated via a simple solution‐processing method. Owing to the improved light absorption by the pyramid structure, the narrowed bandgap of the MoS2 by the imperfect crystallinity, and the enhanced charge separation/transportation by the inserted reduced graphene oxide (RGO), the assembled photodetector exhibits excellent performance in terms of a large responsivity of 21.8 A W?1, extremely high detectivity up to 3.8 × 1015 Jones (Jones = cm Hz1/2 W?1) and ultrabroad spectrum response ranging from 350 nm (ultraviolet) to 4.3 µm (midwave infrared). These device parameters represent the best results for MoS2‐based self‐driven photodetectors, and the detectivity value sets a new record for the 2DMD‐based photodetectors reported thus far. Prospectively, the design of novel 3D heterojunction can be extended to other 2DMDs, opening up the opportunities for a host of high‐performance optoelectronic devices.  相似文献   

16.
2D layers of metal dichalcogenides are of considerable interest for high‐performance electronic devices for their unique electronic properties and atomically thin geometry. 2D SnS2 nanosheets with a bandgap of ≈2.6 eV have been attracting intensive attention as one potential candidate for modern electrocatalysis, electronic, and/or optoelectronic fields. However, the controllable growth of large‐size and high‐quality SnS2 atomic layers still remains a challenge. Herein, a salt‐assisted chemical vapor deposition method is provided to synthesize atomic‐layer SnS2 with a large crystal size up to 410 µm and good uniformity. Particularly, the as‐fabricated SnS2 nanosheet‐based field‐effect transistors (FETs) show high mobility (2.58 cm2 V?1 s?1) and high on/off ratio (≈108), which is superior to other reported SnS2‐based FETs. Additionally, the effects of temperature on the electrical properties are systematically investigated. It is shown that the scattering mechanism transforms from charged impurities scattering to electron–phonon scattering with the temperature. Moreover, SnS2 can serve as an ideal material for energy storage and catalyst support. The high performance together with controllable growth of SnS2 endow it with great potential for future applications in electrocatalysis, electronics, and optoelectronics.  相似文献   

17.
Optoelectronic devices based on metal halide perovskites, including solar cells and light‐emitting diodes, have attracted tremendous research attention globally in the last decade. Due to their potential to achieve high carrier mobilities, organic–inorganic hybrid perovskite materials can enable high‐performance, solution‐processed field‐effect transistors (FETs) for next‐generation, low‐cost, flexible electronic circuits and displays. However, the performance of perovskite FETs is hampered predominantly by device instabilities, whose origin remains poorly understood. Here, perovskite single‐crystal FETs based on methylammonium lead bromide are studied and device instabilities due to electrochemical reactions at the interface between the perovskite and gold source–drain top contacts are investigated. Despite forming the contacts by a gentle, soft lamination method, evidence is found that even at such “ideal” interfaces, a defective, intermixed layer is formed at the interface upon biasing of the device. Using a bottom‐contact, bottom‐gate architecture, it is shown that it is possible to minimize such a reaction through a chemical modification of the electrodes, and this enables fabrication of perovskite single‐crystal FETs with high mobility of up to ≈15 cm2 V?1 s?1 at 80 K. This work addresses one of the key challenges toward the realization of high‐performance solution‐processed perovskite FETs.  相似文献   

18.
1T‐phase molybdenum disulfide (1T‐MoS2) exhibits superior hydrogen evolution reaction (HER) over 2H‐phase MoS2 (2H‐MoS2). However, its thermodynamic instability is the main drawback impeding its practical application. In this work, a stable 1T‐MoS2 monolayer formed at edge‐aligned 2H‐MoS2 and a reduced graphene oxide heterointerface (EA‐2H/1T/RGO) using a precursor‐in‐solvent synthesis strategy are reported. Theoretical prediction indicates that the edge‐aligned layer stacking can induce heterointerfacial charge transfer, which results in a phase transition of the interfacial monolayer from 2H to 1T that realizes thermodynamic stability based on the adhesion energy between MoS2 and graphene. As an electrocatalyst for HER, EA‐2H/1T/RGO displays an onset potential of ?103 mV versus RHE, a Tafel slope of 46 mV dec?1 and 10 h stability in acidic electrolyte. The unexpected activity of EA‐2H/1T/RGO beyond 1T‐MoS2 is due to an inherent defect caused by the gliding of S atoms during the phase transition from 2H to 1T, leading the Gibbs free energy of hydrogen adsorption (ΔGH*) to decrease from 0.13 to 0.07 eV, which is closest to the ideal value (0.06 eV) of 2H‐MoS2. The presented work provides fundamental insights into the impressive electrochemical properties of HER and opens new avenues for phase transitions at 2D/2D hybrid interfaces.  相似文献   

19.
Mobility is a critical parameter that is routinely used for benchmarking the performance of field‐effect transistors (FETs) based on novel nanomaterials. In fact, mobility values are often used to champion nanomaterials since high‐performance devices necessitate high mobility values. The current belief is that the contacts can only limit the FET performance and hence the extracted mobility is an underestimation of the true channel mobility. However, here, such misconception is challenged through rigorous experimental effort, backed by numerical simulations, to demonstrate that overestimation of mobility occurs in commonly used geometries and in nanomaterials for which the contact interface, contact doping, and contact geometry play a pivotal role. In particular, dual‐gated FETs based on multilayer MoS2 and WSe2 are used as case studies in order to elucidate and differentiate between intrinsic and extrinsic contact effects manifesting in the mobility extraction. The choice of 2D layered transition metal dichalcogenides (TMDCs) as the semiconducting channel is motivated by their potential to replace and/or coexist with Si‐based aging FET technologies. However, the results are equally applicable to nanotube‐ and nanowire‐based FETs, oxide semiconductors, and organic‐material‐based thin‐film FETs.  相似文献   

20.
2D transition metal dichalcogenides are promising channel materials for the next‐generation electronic device. Here, vertically 2D heterostructures, so called van der Waals solids, are constructed using inorganic molybdenum sulfide (MoS2) few layers and organic crystal – 5,6,11,12‐tetraphenylnaphthacene (rubrene). In this work, ambipolar field‐effect transistors are successfully achieved based on MoS2 and rubrene crystals with the well balanced electron and hole mobilities of 1.27 and 0.36 cm2 V?1 s?1, respectively. The ambipolar behavior is explained based on the band alignment of MoS2 and rubrene. Furthermore, being a building block, the MoS2/rubrene ambipolar transistors are used to fabricate CMOS (complementary metal oxide semiconductor) inverters that show good performance with a gain of 2.3 at a switching threshold voltage of ?26 V. This work paves a way to the novel organic/inorganic ultrathin heterostructure based flexible electronics and optoelectronic devices.  相似文献   

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