Browsing by Author "Huang, Jyun-Hong"

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High-conductance Two-dimensional 1T '-MoTe2 Synthesized by Sputtering
(2018-01-01)
Huang, Jyun-Hong
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Hsu, Hao-Hua
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Lee, Yao-Jen
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Hou, Tuo-Hung
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電子工程學系及電子研究所
Among extensively researched 2D-TMDs, MoTe2 is an emerging but understudied material because of the lack of reliable and reproducible synthesis methods. The difficulties of its synthesis originate from the weak Mo-Te bonding energy, which results in the low chemical reactivity of MoTe2. Additionally, compared with other TMDs, MoTe2 is relatively unstable. It easily oxidizes and decomposes at high temperatures, which complicate the synthesis using conventional CVD. We have previously developed a PVD method capable of depositing large-area, high-crystallinity, few-layer 2D MoTe2 without complex designs of gas-phase transport or Mo-Te chemical reaction. MoTe2 is directly sputtered and post-annealed in a 2D encapsulation structure to improve its crystallinity. MoTe2 can be synthesized in either homogeneous semiconducting 2H or metallic 1T' phase by controlling the adequate thermal budget during annealing. This talk will mainly discuss the process optimization and electrical properties of 1T'-MoTe2, which is potentially important in several emerging research fields, including 2D interconnect, topological superconductor, and 2H-1T' in-plane homojunction transistor.
Improved Efficiency of a Large-Area Cu(In,Ga)Se-2 Solar Cell by a Nontoxic Hydrogen-Assisted Solid Se Vapor Selenization Process
(2014-04-09)
Wu, Tsung-Ta
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Hu, Fan
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Huang, Jyun-Hong
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Chang, Chia-ho
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Lai, Chih-chung
A nontoxic hydrogen-assisted solid Se vapor selenization process (HASVS) technique to achieve a large-area (40 X 30 cm(2)) Cu(In,Ga)Se-2 (CIGS) solar panel with enhanced efficiencies from 7.1 to 10.8% (12.0% for active area) was demonstrated. The remarkable improvement of efficiency and fill factor comes from improved open circuit voltage (V-oc) and reduced dark current due to (1) decreased interface recombination raised from the formation of a widened buried homojunction with n-type Cd-cu participation and (2) enhanced separation of electron and hole carriers resulting from the accumulation of Na atoms on the surface of the CIGS film. The effects of microstructural, compositional, and electrical characteristics with hydrogen-assisted Se vapor selenization, including interdiffusion of atoms and formation of buried homojunction, were examined in detail. This methodology can be also applied to CIS (CuInSe2) thin film solar cells with enhanced efficiencies from 5.3% to 8.5% (9.4% for active area) and provides a facile approach to improve quality of CIGS and stimulate the nontoxic progress in the large scale CIGS PV industry.
Large-Area 2D Layered MoTe2 by Physical Vapor Deposition and Solid-Phase Crystallization in a Tellurium-Free Atmosphere
(2017-09-08)
Huang, Jyun-Hong
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Deng, Kuang-Ying
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Liu, Pang-Shiuan
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Wu, Chien-Ting
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Chou, Cheng-Tung
Molybdenum ditelluride (MoTe2) has attracted considerable interest for nanoelectronic, optoelectronic, spintronic, and valleytronic applications because of its modest band gap, high field-effect mobility, large spin-orbit-coupling splitting, and tunable 1T/2H phases. However, synthesizing large-area, high-quality MoTe2 remains challenging. The complicated design of gas-phase reactant transport and reaction for chemical vapor deposition or tellurization is nontrivial because of the weak bonding energy between Mo and Te. This study reports a new method for depositing MoTe2 that entails using physical vapor deposition followed by a postannealing process in a Te-free atmosphere. Both Mo and Te are physically deposited onto the substrate by sputtering a MoTe2 target. A composite SiO2 capping layer is designed to prevent Te sublimation during the postannealing process. The postannealing process facilitates 1T-to-2H phase transition and solid-phase crystallization, leading to the formation of high-crystallinity few-layer 2H-MoTe2 with a field-effect mobility of approximate to 10 cm(2) V-1 s(-1), the highest among all nonexfoliated 2H-MoTe2 currently reported. Furthermore, 2H-MoS2 and Td-WTe2 can be deposited using similar methods. Requiring no transfer or chemical reaction of metal and chalcogen reactants in the gas phase, the proposed method is potentially a general yet simple approach for depositing a wide variety of large-area, high-quality, 2D layered structures.
Large-area few-layer MoS2 deposited by sputtering
(2016-06)
Huang, Jyun-Hong
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Chen, Hsing-Hung
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Liu, Pang-Shiuan
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Lu, Li-Syuan
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Wu, Chien-Ting
Direct magnetron sputtering of transition metal dichalcogenide targets is proposed as a new approach for depositing large-area two-dimensional layered materials. Bilayer to few-layer MoS2 deposited by magnetron sputtering followed by post-deposition annealing shows superior area scalability over 20 cm(2) and layer-by-layer controllability. High crystallinity of layered MoS2 was confirmed by Raman, photo-luminescence, and transmission electron microscopy analysis. The sputtering temperature and annealing ambience were found to play an important role in the film quality. The top-gate field-effect transistor by using the layered MoS2 channel shows typical n-type characteristics with a current on/off ratio of approximately 10(4). The relatively low mobility is attributed to the small grain size of 0.1-1 mu m with a trap charge density in grain boundaries of the order of 10(13) cm(-2).
Polymorphism Control of Layered MoTe2 through Two-Dimensional Solid-Phase Crystallization
(2019-06-19)
Huang, Jyun-Hong
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Hsu, Hao-Hua
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Wang, Ding
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Lin, Wei-Ting
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Cheng, Chun-Cheng
Two-dimensional (2D) molybdenum ditelluride (MoTe2) exhibits an intriguing polymorphic nature, showing stable semiconducting 2H and metallic 1T' phases at room temperature. Polymorphism in MoTe2 presents new opportunities in developing phase-change memory, high- performance transistors, and spintronic devices. However, it also poses challenges in synthesizing homogeneous MoTe2 with a precisely controlled phase. Recently, a new yet simple method using sputtering and 2D solid-phase crystallization (SPC) is proposed for synthesizing high-quality and large-area MoTe2. This study investigates the polymorphism control of MoTe2 synthesis using 2D SPC. The Te/Mo ratio and oxygen content in the as-sputtered films correlate strongly with the final phase and electrical properties of SPC MoTe2. Furthermore, the SPC thermal budget may be exploited for stabilizing a deterministic phase. The comprehensive experiments presented in this work demonstrate the versatile and precise controllability on the MoTe2 phase by using the simple 2D SPC technique.
Toward high efficiency and panel size 30 x 40 cm(2) Cu(I,Ga)Se-2 solar cell: Investigation of modified stacking sequences of metallic precursors and pre-annealing process without Se vapor at low temperature
(2014-11-01)
Wu, Tsung-Ta
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Huang, Jyun-Hong
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Hu, Fan
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Chang, Chia-ho
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Liu, Wen-Long
Modified stacking sequence of precursors and pre-annealing process on Se vapor at low temperature were applied to Cu(ln,Ga)Se-2 (CIGS) solar. The remarkable improvement of efficiency (5.53-10.10% and further 11.04%) and open circuit voltage (0.41 V-0.53 V and further 0.56 V) comes from a compact, smooth microstructure, and modified depth profile of Ga with suitable thickness of CuGa multi-stacking layers in the top of precursors as well as surface bandgap enhancement via pre-nnealing process without Se vapor followed by a specific non-toxic hydrogen-assisted solid Se vapor selenization process. The effects of microstructural, compositional and electrical characteristics of Ga distribution including accumulation and interdiffusion were examined in detail. Finally, a large-area (40 x 30 cm(2)) CIGS solar cell efficiency with improved open circuit voltage (V-OC) and fill factor (FE) of 36% and 14% has been demonstrated, yielding a promising efficiency of similar to 11.04%. (C) 2014 Elsevier Ltd. All rights reserved.