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Han Y, Chae M, Choi D, Song I, Ko C, Cresti A, Theodorou C, Joo MK. Negative Differential Interlayer Resistance in WSe 2 Multilayers via Conducting Channel Migration with Vertical Double-Side Contacts. ACS APPLIED MATERIALS & INTERFACES 2023; 15:58605-58612. [PMID: 38051158 DOI: 10.1021/acsami.3c13699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
The inherent interlayer resistance in two-dimensional (2D) van der Waals (vdW) multilayers is expected to significantly influence the carrier density profile along the thickness, provoking spatial modification and separation of the conducting channel inside the multilayers, in conjunction with the thickness-dependent carrier mobility. However, the effect of the interlayer resistance on the variation in the carrier density profile and its direction along the thickness under different electrostatic bias conditions has been elusive. Here, we reveal the presence of a negative differential interlayer resistance (NDIR) in WSe2 multilayers by considering various contact electrode configurations: (i) bottom contact, (ii) top contact, and (iii) vertical double-side contact (VDC). The contact-structure-dependent shape modification of the transconductance clearly manifests the redistribution of carrier density and indicates the direction of the conducting channel migration along the thickness. Furthermore, the distinct characteristic of the electrically tunable NDIR in 2D WSe2 multilayers is revealed by the observed discrepancy between the top- and bottom-channel resistances determined by four-probe measurements with VDC. Our results provide an optimized device layout and further insights into the distinct carrier transport mechanism in 2D vdW multilayers.
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Affiliation(s)
- Yeongseo Han
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
| | - Minji Chae
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
| | - Dahyun Choi
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
| | - Inseon Song
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
| | - Changhyun Ko
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
- Institute of Advanced Materials and Systems, Sookmyung Women's University, Seoul 04310, Republic of Korea
| | - Alessandro Cresti
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, IMEP-LAHC, Grenoble 38000, France
| | - Christoforos Theodorou
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, IMEP-LAHC, Grenoble 38000, France
| | - Min-Kyu Joo
- Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
- Institute of Advanced Materials and Systems, Sookmyung Women's University, Seoul 04310, Republic of Korea
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2
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Khattak Z, Sajid M, Javed M, Zeeshan Rizvi HM, Awan FS. Mass-Producible 2D Nanocomposite-Based Temperature-Independent All-Printed Relative Humidity Sensor. ACS OMEGA 2022; 7:16605-16615. [PMID: 35601310 PMCID: PMC9118384 DOI: 10.1021/acsomega.2c00850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 04/27/2022] [Indexed: 06/15/2023]
Abstract
Relative humidity sensors are widely studied under the categories of both environmental and biosensors owing to their vast reaching applications. The research on humidity sensors is mainly divided into two concentration areas including novel material development and novel device structure. Another approach focuses on the development of printed sensors with performance comparable to the sensors fabricated via conventional techniques. The major challenges in the research on relative humidity sensors include the range of detection, sensitivity (especially at lower %RH), transient response time, and dependence on temperature. Temperature dependence is one of the least studied parameters in relative humidity sensor development. In this work, relative humidity sensors were fabricated using all-printed approaches that are also compatible with mass production, resulting in low cost and easy development. Laser-induced graphene (LIG)-based printed electrodes were used as the transducers, while the 2D MoS2 and graphene nanocomposite was used as the active layer material with the built-in property of temperature independence. The exfoliation process of 2D MoS2 was based on wet grinding, while graphene for the active layer was obtained by scratching the graphene grown on the polyimide (PI) surface via laser ablation. The resulting sensors showed an excellent output response for a full range of 0%RH to 100%RH, having no dependence on the surrounding temperature, and excellent response and recovery times of 4 and 2 s, respectively. The developed sensors can be confidently employed for a wide range of humidity sensing applications where the temperature of the surrounding environment is not constant.
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Aftab S, Samiya M, Hussain MS, Elahi E, Yousuf S, Ajmal HMS, Iqbal MW, Iqbal MZ. ReSe 2/metal interface for hydrogen gas sensing. J Colloid Interface Sci 2021; 603:511-517. [PMID: 34214725 DOI: 10.1016/j.jcis.2021.06.117] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 06/18/2021] [Accepted: 06/20/2021] [Indexed: 11/27/2022]
Abstract
The Fermi level alignment between electrodes and two-dimensional (2D) materials is significant in characterizing sensors based on their reversibility, response time, sensitivity, and long-term stability. Here, we have demonstrated that the modulation of the Schottky barrier height between the interface of metal (Pd/Au) and multilayered ReSe2 nanoflakes caused the change in the transfer curve (Ids-Vbg) of FETs based devices and rectifying characteristics (Ids-Vds) of the Schottky diodes at various hydrogen concentrations at T = 22 °C, fluctuating from 50 to 350 ppm with a response (R%) from 669 to 1198%, respectively. Sensors based on a mono- or bilayer system did not exhibit sensitivity to hydrogen gas owing to metal electrodes diffused into materials. The value of the ideality factor of the Schottky diode-based sensor changed from 4 to 1.6 as the hydrogen concentration was changed from 50 to 900 ppm, while the relative response increased from 0 to 3.5 as the hydrogen concentration was increased from 0 to 900 ppm. This research can offer a real solution for developing cost-effective, faster, and room temperature sensors based on 2D materials.
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Affiliation(s)
- Sikandar Aftab
- Department of Engineering Science, Simon Fraser University, Burnaby, Canada.
| | - Ms Samiya
- Department of Environment and Energy, Sejong University, 209 Neungdong-ro, Gwangjin-gu, South Korea.
| | | | - Ehsan Elahi
- Department of Physics, Sejong University, South Korea.
| | - Saqlain Yousuf
- Deparment of Physics, Sungkyunkwan University, Suwon 440-746, South Korea.
| | | | - Muhammad Waqas Iqbal
- Department of Physics, Riphah International University, 14 Ali Road, Lahore, Pakistan.
| | - Muhammad Zahir Iqbal
- Nanotechnology Research Laboratory, Faculty of Engineering Sciences, GIK Institute of Engineering Sciences and Technology, Topi 23640, Khyber Pakhtunkhwa, Pakistan.
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Vaknin Y, Dagan R, Rosenwaks Y. Schottky Barrier Height and Image Force Lowering in Monolayer MoS 2 Field Effect Transistors. NANOMATERIALS 2020; 10:nano10122346. [PMID: 33255993 PMCID: PMC7761329 DOI: 10.3390/nano10122346] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Revised: 11/18/2020] [Accepted: 11/23/2020] [Indexed: 11/16/2022]
Abstract
Understanding the nature of the barrier height in a two-dimensional semiconductor/metal interface is an important step for embedding layered materials in future electronic devices. We present direct measurement of the Schottky barrier height and its lowering in the transition metal dichalcogenide (TMD)/metal interface of a field effect transistor. It is found that the barrier height at the gold/ single-layer molybdenum disulfide (MoS2) interfaces decreases with increasing drain voltage, and this lowering reaches 0.5-1 V We also show that increase of the gate voltage induces additional barrier lowering.
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Sun H, Zhou X, Wang X, Xu L, Zhang J, Jiang K, Shang L, Hu Z, Chu J. P-N conversion of charge carrier types and high photoresponsive performance of composition modulated ternary alloy W(S xSe 1-x) 2 field-effect transistors. NANOSCALE 2020; 12:15304-15317. [PMID: 32648866 DOI: 10.1039/d0nr04633g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Transition metal dichalcogenides (TMDs) have emerged as a new class of two-dimensional (2D) materials, which are promising for diverse applications in nanoelectronics, optoelectronics, and photonics. To satisfy the requirements of the building blocks of functional devices, systematic modulation of the band gap and carrier type of TMDs materials becomes a significant challenge. Here, we report a salt-assisted chemical vapor deposition (CVD) approach for the simultaneous growth of alloy W(SxSe1-x)2 nanosheets with variable alloy compositions. Electrical transport studies based on the as-fabricated W(SxSe1-x)2 nanosheet field-effect transistors (FETs) demonstrate that charge carrier types of alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. Temperature-dependent current measurement shows that the main scattering mechanism is the charged impurity scattering. The effective Schottky barrier heights of bipolar W(SxSe1-x)2 transistors are initially increased and then decreased with increasing positive (or negative) gate voltage, which is tunable by varying the alloy composition. In addition, the tunability of these W(SxSe1-x)2-based ambipolar transistors is suitable for logic and analog applications and represents a critical step toward future fundamental studies as well as for the rational design of new 2D electronics with tailored spectral responses, and simpler and higher integration densities. Finally, the high photoresponsivity (up to 914 mA W-1) and detectivity (4.57 × 1010 Jones) of ultrathin W(SxSe1-x)2 phototransistors imply their potential applications in flexible light-detection and light-harvesting devices. These band gap engineered 2D structures could open up an exciting opportunity and contribute to finding diverse applications in future functional electronic/optoelectronic devices.
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Affiliation(s)
- Huimin Sun
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Xin Zhou
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Xiang Wang
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Liping Xu
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Jinzhong Zhang
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Kai Jiang
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Liyan Shang
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China.
| | - Zhigao Hu
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China and Shanghai Institute of Intelligent Electronics & Systems, Fudan University, Shanghai 200433, China
| | - Junhao Chu
- Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai), Engineering Research Center of Nanophotonics & Advanced Instrument (Ministry of Education), Department of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China and Shanghai Institute of Intelligent Electronics & Systems, Fudan University, Shanghai 200433, China
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Yan W, Lv C, Zhang D, Chen Y, Zhang L, Ó Coileáin C, Wang Z, Jiang Z, Hung KM, Chang CR, Wu HC. Enhanced NO 2 Sensitivity in Schottky-Contacted n-Type SnS 2 Gas Sensors. ACS APPLIED MATERIALS & INTERFACES 2020; 12:26746-26754. [PMID: 32426961 DOI: 10.1021/acsami.0c07193] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Layered materials are highly attractive in gas sensor research due to their extraordinary electronic and physicochemical properties. The development of cheaper and faster room-temperature detectors with high sensitivities especially in the parts per billion level is the main challenge in this rapidly developing field. Here, we show that sensitivity to NO2 (S) can be greatly improved by at least two orders of magnitude using an n-type electrode metal. Unconventionally for such devices, the ln(S) follows the classic Langmuir isotherm model rather than S as is for a p-type electrode metal. Excellent device sensitivities, as high as 13,000% for 9 ppm and 97% for 1 ppb NO2, are achieved with Mn electrodes at room temperature, which can be further tuned and enhanced with the application of a bias. Long-term stability, fast recovery, and strong selectivity toward NO2 are also demonstrated. Such impressive features provide a real solution for designing a practical high-performance layered material-based gas sensor.
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Affiliation(s)
- Wenjie Yan
- School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
| | - Chengzhai Lv
- School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
| | - Duan Zhang
- Elementary Educational College, Beijing key Laboratory for Nano-Photonics and Nano-Structure, Capital Normal University, Beijing 100048, P. R. China
| | - Yanhui Chen
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Lei Zhang
- Foshan (Southern China) Institute for New Materials, Guangdong 528000, China
| | - Cormac Ó Coileáin
- CRANN and AMBER, School of Chemistry, Trinity College, Dublin Dublin 2, Ireland
| | - Zhi Wang
- School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
| | - Zhaotan Jiang
- School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
| | - Kuan-Ming Hung
- Department of Electronics Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 807, Taiwan, ROC
| | - Ching-Ray Chang
- Department of Physics, National Taiwan University, Taipei 106, Taiwan
| | - Han-Chun Wu
- School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
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7
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Giannazzo F, Schilirò E, Greco G, Roccaforte F. Conductive Atomic Force Microscopy of Semiconducting Transition Metal Dichalcogenides and Heterostructures. NANOMATERIALS 2020; 10:nano10040803. [PMID: 32331313 PMCID: PMC7221570 DOI: 10.3390/nano10040803] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 04/16/2020] [Accepted: 04/17/2020] [Indexed: 11/16/2022]
Abstract
Semiconducting transition metal dichalcogenides (TMDs) are promising materials for future electronic and optoelectronic applications. However, their electronic properties are strongly affected by peculiar nanoscale defects/inhomogeneities (point or complex defects, thickness fluctuations, grain boundaries, etc.), which are intrinsic of these materials or introduced during device fabrication processes. This paper reviews recent applications of conductive atomic force microscopy (C-AFM) to the investigation of nanoscale transport properties in TMDs, discussing the implications of the local phenomena in the overall behavior of TMD-based devices. Nanoscale resolution current spectroscopy and mapping by C-AFM provided information on the Schottky barrier uniformity and shed light on the mechanisms responsible for the Fermi level pinning commonly observed at metal/TMD interfaces. Methods for nanoscale tailoring of the Schottky barrier in MoS2 for the realization of ambipolar transistors are also illustrated. Experiments on local conductivity mapping in monolayer MoS2 grown by chemical vapor deposition (CVD) on SiO2 substrates are discussed, providing a direct evidence of the resistance associated to the grain boundaries (GBs) between MoS2 domains. Finally, C-AFM provided an insight into the current transport phenomena in TMD-based heterostructures, including lateral heterojunctions observed within MoxW1-xSe2 alloys, and vertical heterostructures made by van der Waals stacking of different TMDs (e.g., MoS2/WSe2) or by CVD growth of TMDs on bulk semiconductors.
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8
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Chiang SY, Li YY, Shen TL, Hofmann M, Chen YF. 2D Material-Enabled Nanomechanical Bolometer. NANO LETTERS 2020; 20:2326-2331. [PMID: 32186886 DOI: 10.1021/acs.nanolett.9b04693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We here describe a novel type of long-wavelength radiation detector that measures illumination intensity at room temperature through mechanical transduction. Compared to semiconductor-based bolometers, our nanomechanical detector exhibits low measurement noise and is inherently transparent and flexible. The presented solid-state device is based on a 2D-material film that acts as radiation absorber and detector of mechanical strain at the substrate-absorber interface. Optimization of the 2D material properties and realization of a novel edge-on device geometry combines unprecedented detectivity of 3.34 × 108 cm Hz1/2 W-1 with micrometer-scale spatial resolution. The observed combination of superior performance with the facile and scalable fabrication using only liquid processes shows the potential of the presented detector for future ubiquitous and wearable electronics.
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Affiliation(s)
- Shu-Yuan Chiang
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Yueh-Yuan Li
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Tien-Lin Shen
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Mario Hofmann
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Yang-Fang Chen
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
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9
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Urban F, Lupina G, Grillo A, Martucciello N, Di Bartolomeo A. Contact resistance and mobility in back-gate graphene transistors. NANO EXPRESS 2020. [DOI: 10.1088/2632-959x/ab7055] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
The metal-graphene contact resistance is one of the major limiting factors toward the technological exploitation of graphene in electronic devices and sensors. High contact resistance can be detrimental to device performance and spoil the intrinsic great properties of graphene. In this paper, we fabricate back-gate graphene field-effect transistors with different geometries to study the contact and channel resistance as well as the carrier mobility as a function of gate voltage and temperature. We apply the transfer length method and the y-function method showing that the two approaches can complement each other to evaluate the contact resistance and prevent artifacts in the estimation of carrier mobility dependence on the gate-voltage. We find that the gate voltage modulates both the contact and the channel resistance in a similar way but does not change the carrier mobility. We also show that raising the temperature lowers the carrier mobility, has a negligible effect on the contact resistance, and can induce a transition from a semiconducting to a metallic behavior of the graphene sheet resistance, depending on the applied gate voltage. Finally, we show that eliminating the detrimental effects of the contact resistance on the transistor channel current almost doubles the carrier field-effect mobility and that a competitive contact resistance as low as 700 Ω·μm can be achieved by the zig-zag shaping of the Ni contact.
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10
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Kim Y, Kang SK, Oh NC, Lee HD, Lee SM, Park J, Kim H. Improved Sensitivity in Schottky Contacted Two-Dimensional MoS 2 Gas Sensor. ACS APPLIED MATERIALS & INTERFACES 2019; 11:38902-38909. [PMID: 31592637 DOI: 10.1021/acsami.9b10861] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Two-dimensional (2D) transition-metal dichalcogenides have attracted significant attention as gas-sensing materials owing to their superior responsivity at room temperature and their possible application as flexible electronic devices. Especially, reliable responsivity and selectivity for various environmentally harmful gases are the main requirements for the future chemiresistive-type gas sensor applications. In this study, we demonstrate improved sensitivity of a 2D MoS2-based gas sensor by controlling the Schottky barrier height. Chemical vapor deposition process was performed at low temperature to obtain layer-controlled 2D MoS2, and the NO2 gas responsivity was confirmed by the fabricated gas sensor. Then, the number of MoS2 layers was fixed and the types of electrode materials were varied for controlling the Schottky barrier height. As the Schottky barrier height increased, the NO2 responsivity increased, and it was found to be effective for CO and CO2 gases, which had little reactivity in 2D MoS2-based gas sensors.
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Affiliation(s)
- Youngjun Kim
- School of Electrical and Electronic Engineering , Yonsei University , Seoul 120-749 , Korea
| | - Sang-Koo Kang
- School of Electrical and Electronic Engineering , Yonsei University , Seoul 120-749 , Korea
| | - Nan-Cho Oh
- Korea Sensor Lab , Daejeon 305-701 , Korea
| | - Hi-Deok Lee
- Korea Sensor Lab , Daejeon 305-701 , Korea
- Department of Electronics Engineering , Chungnam National University , Daejeon 305-764 , Korea
| | | | - Jusang Park
- School of Electrical and Electronic Engineering , Yonsei University , Seoul 120-749 , Korea
| | - Hyungjun Kim
- School of Electrical and Electronic Engineering , Yonsei University , Seoul 120-749 , Korea
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11
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Freedy KM, Zhang H, Litwin PM, Bendersky LA, Davydov AV, McDonnell S. Thermal Stability of Titanium Contacts to MoS 2. ACS APPLIED MATERIALS & INTERFACES 2019; 11:35389-35393. [PMID: 31468959 PMCID: PMC7717568 DOI: 10.1021/acsami.9b08829] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Thermal annealing of Ti contacts is commonly implemented in the fabrication of MoS2 devices; however, its effects on interface chemistry have not been previously reported in the literature. In this work, the thermal stability of titanium contacts deposited on geological bulk single crystals of MoS2 in ultrahigh vacuum (UHV) is investigated with X-ray photoelectron spectroscopy and scanning transmission electron microscopy (STEM). In the as-deposited condition, the reaction of Ti with MoS2 is observed resulting in a diffuse interface between the two materials that comprises metallic molybdenum and titanium sulfide compounds. Annealing Ti/MoS2 sequentially at 100, 300, and 600 °C for 30 min in UHV results in a gradual increase in the reaction products as measured by XPS. Accordingly, STEM reveals the formation of a new ordered phase and a Mo-rich layer at the interface following heating. Due to the high degree of reactivity, the Ti/MoS2 interface is not thermally stable even at a transistor operating temperature of 100 °C, while post-deposition annealing further enhances the interfacial reactions. These findings have important consequences for electrical transport properties, highlighting the importance of interface chemistry in the metal contact design and fabrication.
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Affiliation(s)
- Keren M. Freedy
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Huairuo Zhang
- Theiss Research, Inc., La Jolla, California 92037, United States
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, United States
- Corresponding Authors (Z.H.)., (S.McD.)
| | - Peter M. Litwin
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Leonid A. Bendersky
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, United States
| | - Albert V. Davydov
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, United States
| | - Stephen McDonnell
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
- Corresponding Authors (Z.H.)., (S.McD.)
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12
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Di Bartolomeo A, Urban F, Passacantando M, McEvoy N, Peters L, Iemmo L, Luongo G, Romeo F, Giubileo F. A WSe 2 vertical field emission transistor. NANOSCALE 2019; 11:1538-1548. [PMID: 30629066 DOI: 10.1039/c8nr09068h] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We report the first observation of a gate-controlled field emission current from a tungsten diselenide (WSe2) monolayer, synthesized by chemical-vapour deposition on a SiO2/Si substrate. Ni contacted WSe2 monolayer back-gated transistors, under high vacuum, exhibit n-type conduction and drain-bias dependent transfer characteristics, which are attributed to oxygen/water desorption and drain induced Schottky barrier lowering, respectively. The gate-tuned n-type conduction enables field emission, i.e. the extraction of electrons by quantum tunnelling, even from the flat part of the WSe2 monolayers. Electron emission occurs under an electric field ∼100 V μm-1 and exhibits good time stability. Remarkably, the field emission current can be modulated by the back-gate voltage. The first field-emission vertical transistor based on the WSe2 monolayer is thus demonstrated and can pave the way to further optimize new WSe2 based devices for use in vacuum electronics.
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Affiliation(s)
- Antonio Di Bartolomeo
- Physics Department "E. R. Caianiello", University of Salerno, via Giovanni Paolo II n. 132, Fisciano 84084, Italy.
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13
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Progress in Contact, Doping and Mobility Engineering of MoS2: An Atomically Thin 2D Semiconductor. CRYSTALS 2018. [DOI: 10.3390/cryst8080316] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Atomically thin molybdenum disulfide (MoS2), a member of the transition metal dichalcogenide (TMDC) family, has emerged as the prototypical two-dimensional (2D) semiconductor with a multitude of interesting properties and promising device applications spanning all realms of electronics and optoelectronics. While possessing inherent advantages over conventional bulk semiconducting materials (such as Si, Ge and III-Vs) in terms of enabling ultra-short channel and, thus, energy efficient field-effect transistors (FETs), the mechanically flexible and transparent nature of MoS2 makes it even more attractive for use in ubiquitous flexible and transparent electronic systems. However, before the fascinating properties of MoS2 can be effectively harnessed and put to good use in practical and commercial applications, several important technological roadblocks pertaining to its contact, doping and mobility (µ) engineering must be overcome. This paper reviews the important technologically relevant properties of semiconducting 2D TMDCs followed by a discussion of the performance projections of, and the major engineering challenges that confront, 2D MoS2-based devices. Finally, this review provides a comprehensive overview of the various engineering solutions employed, thus far, to address the all-important issues of contact resistance (RC), controllable and area-selective doping, and charge carrier mobility enhancement in these devices. Several key experimental and theoretical results are cited to supplement the discussions and provide further insight.
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14
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15
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Giannazzo F, Fisichella G, Greco G, Di Franco S, Deretzis I, La Magna A, Bongiorno C, Nicotra G, Spinella C, Scopelliti M, Pignataro B, Agnello S, Roccaforte F. Ambipolar MoS 2 Transistors by Nanoscale Tailoring of Schottky Barrier Using Oxygen Plasma Functionalization. ACS APPLIED MATERIALS & INTERFACES 2017; 9:23164-23174. [PMID: 28603968 DOI: 10.1021/acsami.7b04919] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
One of the main challenges to exploit molybdenum disulfide (MoS2) potentialities for the next-generation complementary metal oxide semiconductor (CMOS) technology is the realization of p-type or ambipolar field-effect transistors (FETs). Hole transport in MoS2 FETs is typically hampered by the high Schottky barrier height (SBH) for holes at source/drain contacts, due to the Fermi level pinning close to the conduction band. In this work, we show that the SBH of multilayer MoS2 surface can be tailored at nanoscale using soft O2 plasma treatments. The morphological, chemical, and electrical modifications of MoS2 surface under different plasma conditions were investigated by several microscopic and spectroscopic characterization techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), conductive AFM (CAFM), aberration-corrected scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). Nanoscale current-voltage mapping by CAFM showed that the SBH maps can be conveniently tuned starting from a narrow SBH distribution (from 0.2 to 0.3 eV) in the case of pristine MoS2 to a broader distribution (from 0.2 to 0.8 eV) after 600 s O2 plasma treatment, which allows both electron and hole injection. This lateral inhomogeneity in the electrical properties was associated with variations of the incorporated oxygen concentration in the MoS2 multilayer surface, as shown by STEM/EELS analyses and confirmed by ab initio density functional theory (DFT) calculations. Back-gated multilayer MoS2 FETs, fabricated by self-aligned deposition of source/drain contacts in the O2 plasma functionalized areas, exhibit ambipolar current transport with on/off current ratio Ion/Ioff ≈ 103 and field-effect mobilities of 11.5 and 7.2 cm2 V-1 s-1 for electrons and holes, respectively. The electrical behavior of these novel ambipolar devices is discussed in terms of the peculiar current injection mechanisms in the O2 plasma functionalized MoS2 surface.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Michelangelo Scopelliti
- Dipartimento di Fisica e Chimica (DiFC), Università degli Studi di Palermo , Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
- Aten Center, Università di Palermo , Ed. 18 V.le delle Scienze, Parco d'Orleans II, 90128 Palermo, Italy
- Consorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sistemi Biologici (C.I.R.C.M.S.B.) , 1, Piazza Umberto I, 70121 Bari, Italy
| | - Bruno Pignataro
- Dipartimento di Fisica e Chimica (DiFC), Università degli Studi di Palermo , Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
- Aten Center, Università di Palermo , Ed. 18 V.le delle Scienze, Parco d'Orleans II, 90128 Palermo, Italy
| | - Simonpietro Agnello
- Dipartimento di Fisica e Chimica (DiFC), Università degli Studi di Palermo , Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
- Aten Center, Università di Palermo , Ed. 18 V.le delle Scienze, Parco d'Orleans II, 90128 Palermo, Italy
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