Browsing by Author "Wu, Chong-Rong"

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Enhancement of field-effect mobility in molybdenum-disulfide transistor through the treatment of low-power oxygen plasma
(2016-09)
Chen, Kuan-Chao
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Wu, Chong-Rong
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Chang, Xiang-Rui
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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
Large-Area and Strain-Reduced Two-Dimensional Molybdenum Disulfide Monolayer Emitters on a Three-Dimensional Substrate
(2019-07-24)
Chang, Chiao-Yun
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Lin, Hsiang-Ting
;
Lai, Ming-Sheng
;
Yu, Cheng-Li
;
Wu, Chong-Rong
Atomically thin membranes of two-dimensional (2-D) transition-metal dichalcogenides (TMDCs) have distinct emission properties, which can be utilized for realizing ultrathin optoelectronic integrated systems in the future. Growing a large-area and strain-reduced monolayer 2-D material on a three-dimensional (3-D) substrate with microstructures or nanostructures is a crucial technique because the electronic band structure of TMDC atomic layers is strongly affected by the number of stacked layers and strain. In this study, a large-area and strain-reduced MoS2 monolayer was fabricated on a 3D substrate through a two-step growth procedure. The material characteristics and optical properties of monolayer TMDCs fabricated on the nonplanar substrate were examined. The growth of monolayer MoS2 on a cone-shaped sapphire substrate effectively reduced the tensile strain induced by the substrate by decreasing the thermal expansion mismatch between the 2-D material and the substrate. Monolayer MoS2 grown on the nonplanar substrate exhibited uniform strain reduction and luminescence intensity. The fabrication of monolayer MoS2 on a nonplanar substrate increased the light extraction efficiency. In the future, large-area and strain-reduced 2-D TMDC materials grown on a nonplanar substrate can be employed as novel light-emitting devices for applications in lighting, communication, and displays for the development of ultrathin optoelectronic integrated systems.
Luminescence Enhancement and Enlarged Dirac Point Shift of MoS2/Graphene Hetero-Structure Photodetectors With Postgrowth Annealing Treatment
(2017-01-02)
Wu, Chong-Rong
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Liao, Kun-Cheng
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Wu, Chao-Hsin
;
Lin, Shih-Yen
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影像與生醫光電研究所
Enhanced photoluminescence intensities are observed for the MoS2 film prepared by chemical vapor deposition (CVD) with an additional 850 degrees C postgrowth annealing procedure under sulfur-rich environment. The enlarged Dirac point shift of the MoS2/graphene hetero-structure photodetectors with the postgrowth annealing procedure suggests that more photoexcited electrons will transport to the graphene and effectively higher n-type doped the channel. The direct 2-D crystal hetero-structure growth by using CVD has avoided the complicated procedure of sequential attachment of different 2-D crystals, which is advantageous for the practical application of 2-D crystal heterostructures.
Multilayer MoS2 prepared by one-time and repeated chemical vapor depositions: anomalous Raman shifts and transistors with high ON/OFF ratio
(2015-11-04)
Wu, Chong-Rong
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Chang, Xiang-Rui
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Chang, Shu-Wei
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Chang, Chung-En
;
Wu, Chao-Hsin
We show that multilayer molybdenum disulfide (MoS2) grown with the chemical vapor deposition (CVD) may exhibit quite distinct behaviors of Raman shifts from those of exfoliated ones. The anomalous Raman shifts depend on CVD growth modes and are attributed to the modified dielectric screening and interlayer coupling of MoS2 in various growth conditions. With repeated CVD growths, we demonstrated the precise control over the layer number of MoS2. A decently large drain current, high ON/OFF ratio of 10(5), and enhanced field-effect mobility can be achieved in transistors fabricated on the six-layer MoS2.
Single-Crystal Antimonene Films Prepared by Molecular Beam Epitaxy: Selective Growth and Contact Resistance Reduction of the 2D Material Heterostructure
(2018-05-02)
Chen, Hsuan-An
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Sun, Hsu
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Wu, Chong-Rong
;
Wang, Yu-Xuan
;
Lee, Po-Hsiang
Single-crystal antimonene flakes are observed on sapphire substrates after the postgrowth annealing procedure of amorphous antimony (Sb) droplets prepared by using molecular beam epitaxy at room temperature. The large wetting angles of the antimonene flakes to the sapphire substrate suggest that an alternate substrate should be adopted to obtain a continuous antimonene film. By using a bilayer MoS2/sapphire sample as the new substrate, a continuous and single-crystal antimonene film is obtained at a low growth temperature of 200 degrees C. The results are consistent with the theoretical prediction of the lower interface energy between antimonene and MoS2. The different interface energies of antimonene between sapphire and MoS2 surfaces lead to the selective growth of antimonene only atop MoS2 surfaces on a prepatterned MoS2/sapphire substrate. With similar sheet resistance to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Compared with Au/Ti electrodes, a specific contact resistance reduction up to 3 orders of magnitude is observed by using the multilayer antimonene as the contact metal to MoS2. The lower contact resistance, the lower growth temperature, and the preferential growth to other 2D materials have made antimonene a promising candidate as the contact metal for 2D material devices.
Strain-reduced and Photoluminescence Enhanced of MoS2 Emitters on Three-Dimensional Substrate
(2020-01-01)
Lee, Andrew Boyi
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Chang, Chiao-Yun
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Lin, Hsiang-Ting
;
Lai, Ming-Sheng
;
Yu, Cheng-Li
Two-dimensional (2D) atomic transition metal dichalcogenides (TMDCs) have distinct emission properties, which can be applied for ultrathin detectors and light-emitters in the future. In this study, strain and photoluminescence of MoS2 monolayer on a 3D substrate through a two-step growth procedure was analyzed. The structural of materials and those optical properties of monolayer TMDCs fabricated on the planar and nonplanar substrate were examined. Monolayer MoS2 grown on the nonplanar substrate exhibited uniform strain reduction and luminescence intensity. The fabrication of monolayer MoS2 on a nonplanar substrate increased the light extraction efficiency. In the future, strain-reduced 2D TMDC materials grown on a nonplanar substrate can be employed as novel light-emitting devices for applications in light-emitters, communication, and displays for ultrathin optoelectronic integrated systems.