Search query: How Good Can Monolayer MoS2 Transistors Be

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abstract: Monolayer molybdenum disulfide (MoS(2) unlike its bulk form, is a direct band gap semiconductor with a band gap of 1.8 eV. Recently, field effect transistors have been demonstrated experimentally using a mechanically exfoliated MoS(2) monolayer, showing promising potential for next generation electronics. Here we project the ultimate performance limit of MoS(2) transistors by using nonequilibrium Green's function based quantum transport simulations. Our simulation results show that the strength of MoS(2) transistors lies in large ON OFF current ratio >10(10) immunity to short channel effects (drain induced barrier lowering ~10 mV/V) and abrupt switching (subthreshold swing as low as 60 mV/decade) Our comparison of monolayer MoS(2) transistors to the state of the art III V materials based transistors, reveals that while MoS(2) transistors may not be ideal for high performance applications due to heavier electron effective mass (m 0.45 m(0) and a lower mobility, they can be an attractive alternative for low power applications thanks to the large band gap and the excellent electrostatic integrity inherent in a two dimensional system.
author_names: Youngki Yoon

Kartik Ganapathi

Sayeef S Salahuddin
title: How good can monolayer MoS2 transistors be?
venue: Nano letters
year: 2011

abstract: Electronic junctions on edge Two dimensional materials such as graphene are attractive materials for making smaller transistors because they are inherently nanoscale and can carry high currents. However, graphene has no band gap and the transistors are "leaky" that is, they are hard to turn off. Related transition metal dichalcogenides (TMDCs) such as molybdenum sulfide have band gaps. Transistors based on these materials can have high ratios of "on" to "off" currents. However, it is often difficult to make a good voltage biased (p n) junction between different TMDC materials. Li et al. succeeded in making p n heterojunctions between two of these materials, molybdenum sulfide and tungsten selenide. They did this not by stacking the layers, which make a weak junction, but by growing molybdenum sulfide on the edge of a triangle of tungsten selenide with an atomically sharp boundary Science, this issue p. 524 The regrowth of the second transition metal dichalcogenide monolayer by edge epitaxy creates a lateral p n heterojunction. Two dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on off current ratios and distinctive electro optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p n rectifying diodes, light emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two step epitaxial growth of lateral WSe2 MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.
author_names: Ming-Yang Li

Yumeng Shi

Chia-Chin Cheng

Yung-Chang Lin

Hao-Lin Tang

Meng-Lin Tsai

Chih-Wei Chu

Kung-Hwa Wei

Jr-hau He

Wen-Hao Chang

Kazu Suenaga

Lain-Jong Li
title: Epitaxial growth of a monolayer WSe2 MoS2 lateral p n junction with an atomically sharp interface
venue: Science
year: 2015

abstract: Controlled substitutional doping of two dimensional (2D) transitional metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p type conductivity in MoS2 and WS2 is challenging due to their natural tendency to form n type vacancy defects. Here, we report versatile growth of p type monolayer WS2 by liquid phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with variable concentrations of substitutionally doped Nb up to 1014 cm 2 can be grown by reacting solution deposited precursor film with sulfur vapor at 850 oC reflecting the good miscibility of the precursors in the liquid phase. Atomic resolution characterization with aberration corrected scanning TEM (STEM) reveals that the Nb concentration can vary by as much as one order of magnitude along the radial direction in some crystals. We also demonstrate that ambipolar field effect transistors can be fabricated based on Nb doped monolayer WS2.
author_names: Ziyu Qin

Leyi Loh

Junyong Wang

Xiaomin Xu

Qicheng Zhang

Benedikt Haas

Carlos Alvarez

Hanako Okuno

Justin Zhou Yong

Thorsten Schultz

Norbert Koch

Jiadong Dan

Stephen John Pennycook

Dawen Zeng

Michel Bosman

Goki Eda
title: Growth of Nb Doped Monolayer WS2 from Liquid Phase Precursor Mixing.
venue: ACS nano
year: 2019

abstract: We report that control over the grain size and lateral growth of monolayer MoS<sub>2</sub> film, yielding a uniform large area monolayer MoS<sub>2</sub> film, can be achieved by submitting the SiO<sub>2</sub> surfaces of the substrates to oxygen plasma treatment and modulating substrate temperature in chemical vapor deposition (CVD) process. Scanning electron microscopy and atomic force microscopy images and Raman spectra revealed that the MoS<sub>2</sub> lateral growth could be controlled by the surface treatment conditions and process temperatures. Moreover, the obtained monolayer MoS<sub>2</sub> films showed excellent scalable uniformity covering a centimeter scale SiO<sub>2</sub> /Si substrates, which was confirmed with Raman and photoluminescence mapping studies. Transmission electron microscopy measurements revealed that the MoS<sub>2</sub> film of the monolayer was largely single crystalline in nature. Back gate field effect transistors based on a CVD grown uniform monolayer MoS<sub>2</sub> film showed a good current on/off ratio of ~10<sup>6</sup> and a field effect mobility of 7.23 cm<sup>2</sup>/V*s. Our new approach to growing MoS<sub>2</sub> films is anticipated to advance studies of MoS<sub>2</sub> or other transition metal dichalcogenide material growth mechanisms and to facilitate the mass production of uniform high quality MoS<sub>2</sub> films for the commercialization of a variety of applications.
author_names: Jaeho Jeon

Sung Kyu Jang

Su Min Jeon

Gwangwe Yoo

Jin-Hong Park

Sungjoo Lee
title: Controlling Grain Size and Continuous Layer Growth in Two Dimensional MoS2 Films for Nanoelectronic Device Application
venue: IEEE Transactions on Nanotechnology
year: 2015

abstract: Two dimensional (2D) semiconducting monolayer transition metal dichalcogenides (TMDCs) have stimulated lots of interest because they are direct bandgap materials that have reasonably good mobility values. However, contact between most metals and semiconducting TMDCs like 2H phase WSe2 are highly resistive, thus degrading the performance of field effect transistors (FETs) fabricated with WSe2 as active channel materials. Recently, a phase engineering concept of 2D MoS2 materials was developed, with improved device performance. Here, we applied this method to chemical vapor deposition (CVD) grown monolayer 2H WSe2 and demonstrated semiconducting to metallic phase transition in atomically thin WSe2. We have also shown that metallic phase WSe2 can be converted back to semiconducting phase, demonstrating the reversibility of this phase transition. In addition, we fabricated FETs based on these CVD grown WSe2 flakes with phase engineered metallic 1T WSe2 as contact regions and intact semiconducting 2H WSe2 as active channel materials. The device performance is substantially improved with metallic phase source/drain electrodes, showing on/off current ratios of 10(7) and mobilities up to 66 cm(2)/V*s for monolayer WSe2. These results further suggest that phase engineering can be a generic strategy to improve device performance for many kinds of 2D TMDC materials.
author_names: Yuqiang Ma

Bilu Liu

Anyi Zhang

Liang Chen

Mohammad Fathi

Chenfei Shen

Ahmad N Abbas

M Ge

Matthew Mecklenburg

Chongwu Zhou
title: Reversible Semiconducting to Metallic Phase Transition in Chemical Vapor Deposition Grown Monolayer WSe2 and Applications for Devices.
venue: ACS nano
year: 2015

abstract: The lack of stable and efficient techniques to synthesize high quality large area thin films is one of the major bottlenecks for the real world application of the 2D transition metal dichalcogenides. In this work, the growth of molybdenum disulfide (MoS2 on sapphire substrates by sulfurizing the MoO3 film deposited by atomic layer deposition (ALD) is reported. The advantages of the ALD method can be well inherited, and the synthesized MoS2 films exhibit excellent layer controllability, wafer scale uniformity, and homogeneity. MoS2 films with desired thickness can be obtained by varying MoO3 ALD cycles. The atomic force microscope and Raman measurements demonstrate that the ALD based MoS2 has good uniformity. Clear Raman shift as a function of the film thickness is observed. Field effect transistor devices are fabricated through a transfer free and top down process. High On/Off current ratio (104 and medium level electron mobilities (0.76 cm2 V 1 s 1 for monolayer, and 5.9 cm2 V 1 s 1 for four layer) are obtained. The work opens up an attractive approach to realize the application of wafer scale 2D materials in integrated circuits and systems.
author_names: Mao-Lin Shi

Lin Chen

Tian-bao Zhang

Jing Xu

Hao Zhu

Qingqing Sun

David-Wei Zhang
title: Top Down Integration of Molybdenum Disulfide Transistors with Wafer Scale Uniformity and Layer Controllability.
venue: Small
year: 2017

abstract: Experimental two dimensional (2D) black phosphorus (BP) transistors typically appear in the form of Schottky barrier field effect transistors (SBFETs) but their performance limit remains open. We investigate the performance limit of monolayer BP SBFETs in the sub 10 nm scale by using ab initio quantum transport simulations. The devices with 2D graphene electrodes are apparently superior to those with bulk Ti electrodes due to their smaller and tunable Schottky barrier heights and the absence of metal induced gap states in the channels. With graphene electrodes, the performance limit of the sub 10 nm monolayer BP SBFETs outperforms the monolayer MoS2, carbon nanotube, and advanced silicon transistors and even can meet the requirements of both high performance and low power logic applications of the next decade in the latest International Technology Roadmap for Semiconductors. It appears that the ML BP SBFETs have the best intrinsic device performance among the reported sub 10 nm 2D material SBFETs.
author_names: Ruge Quhe

Xiyou Peng

Yuanyuan Pan

Meng Ye

Han Zhang

Shenyan Feng

Qiaoxuan Zhang

Jun-jie Shi

Jinbo Yang

Dapeng Yu

Minglong Lei

Jing Lu
title: Can a Black Phosphorus Schottky Barrier Transistor Be Good Enough?
venue: ACS applied materials interfaces
year: 2017

abstract: Among a variety of 2D graphene like materials, molybdenum disulfide (MoS2) stands out due to its remarkable physical, electrical, and optical properties [1] The existence of a direct bandgap in the MoS2 monolayer offers an attractive possibility of using this material in field effect transistors and optoelectronic devices. Furthermore, MoS2 can produce high specific area nanostructures and has reasonably good electrochemical performance, the desirable features for application in energy storage devices [2] However, the mass production of large area electrodes based on MoS2 has been a major hurdle for their practical applications.
author_names: Maykel dos Santos Klem

Gabriel Leonardo Nogueira

C R C Sousa

Neri Alves
title: Spray printed molybdenum disulfide electrodes for application in supercapacitors
year: 2019

abstract: We present ab initio calculations of uniaxial absolute deformation potentials of the valence and the conduction bands in monolayer MoS2, MoSe2, WS2, WSe2, h BN, and phosphorene. Calculations are performed using both semilocal and hybrid functionals. The absolute positions of the band edges in strained and unstrained materials are determined using the vacuum level as reference. For WSe2, we compare the obtained results with measured shifts of the valence band maximum (VBM) and the conduction band minimum (CBM) induced by uniaxial strain and find a very good agreement. The parameters describing the shifts in the VBM and CBM positions under strain can be used in the modeling of devices such as tunneling field effect transistors.
author_names: Julia Wiktor

Alfredo Pasquarello
title: Absolute deformation potentials of two dimensional materials
year: 2016

abstract: Atomically thin MoS2 has drawn tremendous attention due to its great potential in a range of electronic devices such as photodetectors, field effect transistors (FET) and sensors. In the past few years, numerous methods including mechanical cleavage, liquid exfoliation, chemical vapor deposition (CVD) have been devoted to synthesizing two dimensional atomically thin MoS2. Among these methods, CVD is the most promising method for preparing large size and highly crystalline MoS2 monolayers, exhibiting relatively good optical and electrical properties. Nevertheless, there are so many experiment parameters in CVD process that we should take into account, which makes it still a challenge for us to grow large scale, single crystalline MoS2 monolayer films suitable for practical applications. This review systematically summarized some synthetic strategies of MoS2 by CVD in recent years. We also discussed in detail how these vital factors such as substrates, carrier gases, Mo precursors, influenced the process of growth, which was expected to help us to controllably synthesize high quality MoS2 and other kinds of transition metal dichalcogenides including WS2, VS2, WSe2 and so forth.
author_names: Wei Li

Yanglong Hou
title: Review: Controllable Synthesis of Two Dimensional (2D) MoS 2 by Chemical Vapor Deposition Process
year: 2018