Browsing by Author "Yang, Chun-Chuen"

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Intriguing field-effect-transistor performance of two-dimensional layered and crystalline CrI3
(2020-03-01)
Patil, Ranjit A.
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Tu, Hao-Wei
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Jen, Ming-Hsing
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Lin, Jing-Jia
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Wu, Ching-Cherng
There are many candidate materials that can be used as channel materials for the next-generation field effect transistors (FETs). CrI3 is one of the particular candidates for application in FET, because it is a two-dimensional (2D) ferromagnet and has giant tunneling magnetoresistance. The ferromagnetic nature extends to not only electronics but also spintronics. In this study, the large-area, layered, and crystalline 2D CrI3 were synthesized by horizontal Bridgman method. The suspended CrI3 FETs were fabricated for explorations of intrinsic electron transport in the CrI3 channel and of electrical contact problems. The suspended FET structure lets the CrI3 channel free from trapping charges in the SiO2-capped Si substrate. The oneoff ratio of the suspended CrI3 FET is up to 10(4), making the 2D layered CrI3 potential for future FETs. The investigations of the mobility and the interface-trap density at various temperatures reveal that the trapping charges as well as the interface-trap densities are increased with further gas adsorption on the surface of the CrI3 flake. The performance of the suspended CrI3 FET can be improved, if the gas adsorption problem can be carefully treated. (c) 2020 Elsevier Ltd. All rights reserved.
P-Type Doping of WS2 Quantum Dots via Pulsed Laser Ablation
(2018-12-01)
Caigas, Septem P.
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Cheng, Min-Chiang
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Lin, Tzu-Neng
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Santiago, Svette Reina Merden S.
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Yuan, Chi-Tsu
Doping provides an advantage to engineering the optical and electrical characteristics of transition-metal dichalcogenides (TMDs). Here, we report the doping of WS2 quantum dots (QDs) with diethylenetriamine (DETA) using pulsed laser ablation. The synthesized DETA-doped 2H-WS2 QDs with an average size of similar to 6 nm have been demonstrated by transmission electron microscopy. With the introduction of DETA during pulsed laser ablation, current modulation, carrier concentration, and field-effect mobility are greatly enhanced, demonstrating a successful doping in WS2 QDs. The positive shift of the threshold voltage in gate dependent conductance measurements reveals p-type doping for DETA-doped WS2 QDs. A remarkable improvement in photoluminescence in WS2 QDs by 74-fold has been achieved after DETA doping. An anomalous dopant-dependent negative photoconductivity was observed for WS2 QDs, originating from light-induced desorbing of water (oxygen) molecules on the surface. The proposed doping approach can provide a vehicle to modulate the optical and electrical properties in WS2 QDs and could be important in the performance improvement of WS2-QD-based devices.
Size effect on multiferroic TbMn2O5 nanorods
(2015-05-07)
Yang, Chun-Chuen
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Tung, Yung-Hsiang
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Chen, Yi-Jung
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Hsu, Ting-Wei
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You, Pang-Yen
The effect of the size of TbMn2O5 on their magnetoelectric properties is studied using a field emission transmission electron microscope, ac magnetic susceptibility, relative dielectric constant, specific heat capacity, and x-ray diffraction at various temperatures. A bulk sample and nanorods with two axial lengths, < L-C >, are investigated. Nanorods with < L-C > of 216 nm and 64 nm crystallize with orthorhombic Pbam symmetry as the bulk material. The axial direction of the two sizes of nanorod is parallel to the c axis of the crystal. No particular radial direction is observed. The critical size for the magnetic ordering of TbMn2O5 is found to be between < L-C > - 64 nm and 216 nm. Experiments on specific heat capacity verified these results. No similar phenomenon concerning the ferroelectric property is observed. At T = 30K and 35 K, the < L-C > - 216 nm sample yields a charge-ordering-like x-ray diffraction peak, which may be associated with the magnetically induced charge ordering superlattice. (C) 2015 AIP Publishing LLC.