Browsing by Author "Lee, Si-Chen"

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Current Enhancement and Bipolar Current Modulation of Top-Gate Transistors Based on Monolayer MoS2 on Three-Layer WxMo1-xS2
(2018-07-25)
Chen, Kuan-Chao
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Jian, Cing-Yu
;
Chen, Yi-Jia
;
Lee, Si-Chen
;
Chang, Shu-Wei
We demonstrated the top-gate transistors composed of monolayer MoS2 grown on three-layer alloys MoxW1-xS2 prepared by sequential sulfurization of predeposited transition metal films. The elemental mapping of the alloy indicates a uniform distribution of both cations Mo and W in the grown samples. Surprisingly, we find that the drain current of transistors could be enhanced by 2 orders of magnitude as the composition of Mo increases, whereas the gate-controlled current modulation turns bipolar and ultimately vanishes. These features might originate from the formation of in-gap defect states, with modest activation energy for transport and moderate hopping probability for current conduction, or a reduced electronic band gap of the conducting channel because of strain.
Enhancement of field-effect mobility in molybdenum-disulfide transistor through the treatment of low-power oxygen plasma
(2016-09)
Chen, Kuan-Chao
;
Wu, Chong-Rong
;
Chang, Xiang-Rui
;
Chang, Shu-Wei
;
Lee, Si-Chen
We experimentally demonstrate that the treatment with low-power oxygen plasma can raise the field-effect mobility in molybdenum-sulfide (MoS2) transistors from 0.01 to 9.6 cm(2)V(-1)s(-1), which is an increment of about three orders of magnitude. The decrease in threshold voltage and the increase in the drain current of the devices indicate that the electron density increases significantly after the mild plasma treatment. The emergence of Mo-O characteristics but the suppression of Mo-S features on the X-ray photoelectron spectrum of the plasma-treated sample suggests that a portion of the MoS2 film becomes conductive molybdenum oxide. This transformation may considerably upgrade the performance of MoS2 transistors. (C) 2016 The Japan Society of Applied Physics
Fermi-level shifts in graphene transistors with dual-cut channels scraped by atomic force microscope tips
(2014-01-13)
Lin, Meng-Yu
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Chen, Yen-Hao
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Su, Chen-Fung
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Chang, Shu-Wei
;
Lee, Si-Chen
We investigate the electronic properties of p-type graphene transistors on silicon dioxide with dual-cut channels that were scraped using atomic force microscope tips. In these devices, the current is forced to squeeze into the path between the two cuts rather than flow directly through the graphene sheet. We observe that the gate voltages with minimum current shift toward zero bias as the sizes of the dual-cut regions increase. These phenomena suggest that the Fermi levels in the dual-cut regions are shifted toward the Dirac points after the mechanical scraping process. (C) 2014 AIP Publishing LLC.
Field effect of in-plane gates with different gap sizes on the Fermi level tuning of graphene channels
(2014-05-05)
Lin, Meng-Yu
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Chen, Yen-Hao
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Wang, Cheng-Hung
;
Su, Chen-Fung
;
Chang, Shu-Wei
Tuning of the Fermi level is investigated in graphene channels using two in-plane gates with significantly different-sized isolating gaps. While the n-type tuning was achievable in both schemes, the wide-gap device had an enhanced minimum drain current and less prominent current modulation than the narrow-gap device. In addition, further p-type tuning was not observed in the wide-gap device at negative gate biases. These phenomena indicated that both devices had distinct field-strength dependences and Fermi level tuning effects, which may be critical for the practical design of devices. (C) 2014 AIP Publishing LLC.
Graphene films grown at low substrate temperature and the growth model by using MBE technique
(2013-09-01)
Lin, Meng-Yu
;
Guo, Wei-Ching
;
Wu, Meng-Hsun
;
Wang, Pro-Yao
;
Lee, Si-Chen
By depositing atomic C atoms on the grained Cu foil by using molecular beam epitaxy technique (MBE), high-quality graphene is obtained at low substrate temperature 300 degrees C. A model of initial graphene flake formation as crystal seeds and following lateral graphene growth is established to explain the growth mechanisms. After atomic C atom deposition, no significant difference is observed before and after MBE growth. The results suggest that the deposition of atomic C atoms will not improve the crystalline quality of pre-formed C films. The low substrate temperature required would be advantageous for the practical application of graphene. (c) 2013 Elsevier B.V. All rights reserved.
Low-temperature grown graphene films by using molecular beam epitaxy
(2012-11-26)
Lin, Meng-Yu
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Guo, Wei-Ching
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Wu, Meng-Hsun
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Wang, Pro-Yao
;
Liu, Te-Huan
Complete graphene film is prepared by depositing carbon atoms directly on Cu foils in a molecular beam epitaxy chamber at 300 degrees C. The Raman spectrum of the film has indicated that high-quality few-layer graphene is obtained. With back-gated transistor architecture, the characteristic current modulation of graphene transistors is observed. Following the similar growth procedure, graphitization is observed at room temperature, which is consistent with the molecular dynamics simulations of graphene growth. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768948]
Painted graphitic carbon films formed underneath Ni templates
(2012)
Lin, Meng-Yu
;
Sheng, Yung-Shuan
;
Lin, Shih-Yen
;
Lee, Si-Chen
;
光電工程學系
By using charcoal pencil as carbon source in the metal-catalyzed crystallization method, graphitic carbon films are demonstrated in this paper. The annealing temperature is the key issue to obtain high-quality graphitic carbon films. The mechanism of metal-catalyzed crystallization of nickel is also investigated. The investigation of fabricate graphene with metal-catalyzed crystallization of pencil carbon make it a low-cost and easy approach for large-area graphene preparation. Also observed is the graphitic carbon film underneath the Ni templates. Compared to the top layer graphene, underneath graphene has better film completeness and similar film quality. With the underneath graphene, selective graphene deposition can be easily achieved by pre-patterning the metal template. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Passivated graphene transistors fabricated on a millimeter-sized single-crystal graphene film prepared with chemical vapor deposition
(2015-07-29)
Lin, Meng-Yu
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Wang, Cheng-Hung
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Chang, Shu-Wei
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Lee, Si-Chen
;
Lin, Shih-Yen
In this work, we first investigate the effects of partial pressures and flow rates of precursors on the single-crystal graphene growth using chemical vapor depositions on copper foils. These factors are shown to be critical to the growth rate, seeding density and size of graphene single crystals. The prepared graphene films in millimeter sizes are then bubbling transferred to silicon-dioxide/silicon substrates for high-mobility graphene transistor fabrications. After high-temperature annealing and hexamethyldisilazane passivation, the water attachment is removed from the graphene channel. The elimination of uncontrolled doping and enhancement of carrier mobility accompanied by these procedures indicate that they are promising for fabrications of graphene transistors.
Plasmonic thermal emitter using perfect absorber made of metallic disk on SiO2
(2012)
Abbas, Mohammed Nadhim
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Cheng, Cheng-Wen
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Chang, Yia-Chung
;
Shih, Min-Hsiung
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Chen, Hung-Hsin
It is shown that the metallic disk structure can be used as an efficient narrow-band thermal emitter in the IR region. The absorption spectra of such structure are investigated both theoretically and experimentally. Calculations of thermal radiation properties of the metallic disk show that the metallic disk is a perfect emitter at a specific wavelength. The metallic disk exhibits only one significant localized surface plasmon polariton mode for both TM and TE polarizations simultaneously.
The growth mechanisms of graphene directly on sapphire substrates by using the chemical vapor deposition
(2014-06-14)
Lin, Meng-Yu
;
Su, Chen-Fung
;
Lee, Si-Chen
;
Lin, Shih-Yen
;
光電工程學系
Uniform and large-area graphene films grown directly on sapphire substrates by using a low-pressure chemical vapor deposition system are demonstrated in this paper. The evolution process and the similar Raman spectra of the samples with different growth durations have confirmed that the continuous graphene film is formed by graphene flakes with similar sizes. The layer-by-layer growth mechanism of this approach is attributed to the preferential graphene deposition on sapphire surfaces. The etching effect of H-2 gas is demonstrated to be advantageous for the larger graphene grain formation. The smooth surface of substrates is also proved to be a key parameter for continuous graphene film formation with better crystalline quality. (C) 2014 AIP Publishing LLC.
Toward epitaxially grown two-dimensional crystal hetero-structures: Single and double MoS2/graphene hetero-structures by chemical vapor depositions
(2014-08-18)
Lin, Meng-Yu
;
Chang, Chung-En
;
Wang, Cheng-Hung
;
Su, Chen-Fung
;
Chen, Chi
Uniform large-size MoS2/graphene hetero-structures fabricated directly on sapphire substrates are demonstrated with layer-number controllability by chemical vapor deposition (CVD). The cross-sectional high-resolution transmission electron microscopy (HRTEM) images provide the direct evidences of layer numbers of MoS2/graphene hetero-structures. Photo-excited electron induced Fermi level shift of the graphene channel are observed on the single MoS2/graphene hetero-structure transistors. Furthermore, double hetero-structures of graphene/MoS2/graphene are achieved by CVD fabrication of graphene layers on top of the MoS2, as confirmed by the cross-sectional HRTEM. These results have paved the possibility of epitaxially grown multi-hetero-structures for practical applications. (C) 2014 AIP Publishing LLC.