Browsing by Author "Wang, Sheng-Wen"

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A Comprehensive Study of One-Step Selenization Process for Cu(In1-xGax) Se-2 Thin Film Solar Cells
(2017-03-21)
Chen, Shih-Chen
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Wang, Sheng-Wen
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Kuo, Shou-Yi
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Juang, Jenh-Yih
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Lee, Po-Tsung
In this work, aiming at developing a rapid and environmental-friendly process for fabricating CuIn1-xGaxSe2 (CIGS) solar cells, we demonstrated the one-step selenization process by using selenium vapor as the atmospheric gas instead of the commonly used H2Se gas. The photoluminescence (PL) characteristics indicate that there exists an optimal location with superior crystalline quality in the CIGS thin films obtained by one-step selenization. The energy dispersive spectroscopy (EDS) reveals that the Ga lateral distribution in the one-step selenized CIGS thin film is intimately correlated to the blue-shifted PL spectra. The surface morphologies examined by scanning electron microscope (SEM) further suggested that voids and binary phase commonly existing in CIGS films could be successfully eliminated by the present one-step selenization process. The agglomeration phenomenon attributable to the formation of MoSe2 layer was also observed. Due to the significant microstructural improvement, the current-voltage (J-V) characteristics and external quantum efficiency (EQE) of the devices made of the present CIGS films have exhibited the remarkable carrier transportation characteristics and photon utilization at the optimal location, resulting in a high conversion efficiency of 11.28%. Correlations between the defect states and device performance of the one-step selenized CIGS thin film were convincingly delineated by femtosecond pump-probe spectroscopy.
A Proposal for Intelligent Agents with Adjusting Self-Reputation Capability for Preventing Fraud in Multi-Agent Societies
(2014-03-01)
Wang, Sheng-Wen
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Huang, Chung-Yuan
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Sun, Chuen-Tsai
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資訊工程學系
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Department of Computer Science
Intelligent agents are increasingly being used for tasks such as e-commerce auto-bidding. Cooperation and defection challenges commonly found in multi-agent systems make the design and construction of a reliable reputation mechanism an important research and engineering goal. Here we describe our proposal for an intelligent agent model that addresses learning issues in terms of self-reputation. The agents in our proposed model are capable of evaluating their behaviors based on a mix of public and private interest considerations, and of testing various solutions aimed at mitigating self-discrepancy and meeting social standards. Our results indicate promise for integrating a self-reputation mechanism into a self-learning framework in a manner that encourages the early emergence of social cooperation among multiple agents and specific cooperation with individual agents.
An indoor light-activated 3D cone-shaped MoS2 bilayer-based NO gas sensor with PPb-level detection at room-temperature
(2019-06-07)
Chen, Yu-Ze
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Wang, Sheng-Wen
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Yang, Chun-Chuan
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Chung, Chieh-Han
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Wang, Yi-Chung
Utilization of light to boost the performance of gas sensors allows us to operate sensor devices at room temperature. Here, we, for the first time, demonstrated an indoor light-activated 3D cone-shaped MoS2 bilayer-based NO gas sensor with ppb-level detection operated at room-temperature. Large-area coneshaped (CS)-MoS2 bilayers were grown by depositing 2 nm-thick MoO3 layers on a 2'' three-dimensional (3D) cone-patterned sapphire substrate (CPSS) followed by a sulfurization process via chemical vapor deposition. Because the exposed area of MoS2 bilayers is increased by 30%, the CS-MoS2 gas sensor (GS) demonstrated excellent performance with a response of 470% and a fast response time of 25 s after exposure to 1 ppm of NO gas illuminated by ultraviolet (UV) light with a wavelength of 365 nm. Such extraordinary performance at room temperature is attributed to the enhanced light absorption because of the light scattering effect caused by the 3D configuration and photo-desorption induced by UV illumination. For NO concentrations ranging from 2 ppm down to 0.06 ppm, the CS-MoS2 GS demonstrated a stable sensing behavior with a high response and fast response time (470% and 25 s at 2 ppm NO) because of the light absorption enhanced by the 3D structure and photo-desorption under constant UV illumination. The CS-MoS2 GS exhibits a high sensitivity (189.2 R% ppm-1), allowing the detection of NO gas at 0.06 ppm in 130 s. In addition, the 3D cone-shaped structure prolonged the presence of sulfur vapor around MoO3, allowing MoO3 to react with sulfur completely. Furthermore, the CS-MoS2 GS using an indoor lighting to detect NO gas at room temperature was demonstrated for the first time where the CS-MoS2 GS exhibits a stable cycling behavior with a high response (165% at 1 ppm NO) in 50 s; for concentration as low as 0.06 ppm, the response of 75% in 150 s can be achieved.
Direct Synthesis and Practical Bandgap Estimation of Multilayer Arsenene Nanoribbons
(2016-01-26)
Tsai, Hsu-Sheng
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Wang, Sheng-Wen
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Hsiao, Ching-Hung
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Chen, Chia-Wei
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Ouyang, Hao
Effect of InGaN/GaN Multiple Quantum Wells with p-n Quantum Barriers on Efficiency Droop in Blue Light-emitting Diodes
(2013-01-01)
Wang, Sheng-Wen
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Lin, Da-Wei
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Lee, Chia-Yu
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Liu, Che-Yu
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Lan, Yu-Pin
In this study, the structures of InGaN/GaN multiple quantum wells (MQWs) with p-n quantum barriers in various positions were proposed to investigate the efficiency droop behavior for blue light-emitting diodes (LEDs). The simulated electric field diagrams showed that the quantum well (QW) sandwiched by the p-n quantum barriers had a less electric field than the other QWs due to the original polarization-related electric field was partially balanced off by the built-in electric field of the p-n quantum barriers. In addition, the simulation results demonstrated that by selecting suitable position of p-n quantum barriers, the distribution of carriers could be effectively improved; hence the droop behavior could also be suppressed.
Effective optimization and analysis of white LED properties by using nano-honeycomb patterned phosphor film
(2016-08-22)
Lin, Huang-Yu
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Wang, Sheng-Wen
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Lin, Chien-Chung
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Tu, Zong-Yi
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Lee, Po-Tsung
This study presents an approach for patterning a polydimethylsiloxane (PDMS) phosphor film with a photonic crystal nano-honeycomb structure on a blue chip package. A phosphor film with a nano-honeycomb structure was patterned and transferred using a nanosphere and used for fabricating remote white light-emitting diodes (w-LEDs). The angular correlated color temperature deviation of the remote phosphor LED could be improved by varying nano-honeycomb structure pitches (450, 750, and 1150 nm). In particular, w-LED samples with excellent color uniformity (Delta CCT ranging from 940 to 440 K) were fabricated from 750-nm w-LED samples with nano-honeycomb-patterned tops. (C) 2016 Optical Society of America
Enhanced power conversion efficiency in InGaN-based solar cells via graded composition multiple quantum wells
(2015-11-30)
Tsai, Yu-Lin
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Wang, Sheng-Wen
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Huang, Jhih-Kai
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Hsu, Lung-Hsing
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Chiu, Ching-Hsueh
This work demonstrates the enhanced power conversion efficiency (PCE) in InGaN/GaN multiple quantum well (MQWs) solar cells with gradually decreasing indium composition in quantum wells (GQWs) toward p-GaN as absorber. The GQW can improve the fill factor from 42% to 62% and enhance the short current density from 0.8 mA/cm(2) to 0.92 mA/cm(2), as compares to the typical MQW solar cells. As a result, the PCE is boosted from 0.63% to 1.11% under AM1.5G illumination. Based on simulation and experimental results, the enhanced PCE can be attributed to the improved carrier collection in GQW caused by the reduction of potential barriers and piezoelectric polarization induced fields near the p-GaN layer. The presented concept paves a way toward highly efficient InGaN-based solar cells and other GaN-related MQW devices. (C) 2015 Optical Society of America
Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate
(2019-02-14)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Medin, Henry
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Chung, Chieh-Han
In the present study, novel MoS2 bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS2 bilayers can be grown conformally on a patterned (cones or pyramids) sapphire substrate without any wrinkles on the 2D film. After the sulfurization process, the MoS2 bilayer is subjected to a local strain in the patterns and its band gap gets enlarged due to the strain. This phenomenon is beneficial for photo-devices to enable the collection of the photocurrent. Measurements revealed a broadband enhancement of the MoS2-based photodetector with a patterned array in terms of both absorption and photocurrent. It is noteworthy that a cone-patterned sapphire substrate (CPSS) is able to generate more photocurrent when illuminated under blue light illumination, whereas the pyramid-patterned sapphire substrate (PPSS) performs best under green and red light illumination. Simulations of the electric field distributions for MoS2 coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS2-based photodetector can be greatly enhanced by the light-scattering effect.
Excellent Color Quality of White-Light-Emitting Diodes by Embedding Quantum Dots in Polymers Material
(2016-01-01)
Lin, Huang-Yu
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Wang, Sheng-Wen
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Lin, Chien-Chung
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Chen, Kuo-Ju
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Han, Hau-Vei
This study employs the polyfluorene composite (called Green B) with several colors of quantum dots to generate the high-color-rendering index (CRI) white LEDs. The Green B polymer is a good candidate to manufacture the hybrid w-LED because of its good quantum efficacy. The hybrid w-LEDs are fabricated by the mixing of Green B with yellow quantum dots and red quantum dots or orange quantum dots to obtain the correlated color temperatures of 3500 and 5500 K. The use of the hybrid polymer/QDs w-LEDs is proved to be beneficial as QD w-LEDs can improve the CRI up to 90 in 3500 K. The luminous efficiency of such devices can be as high as 17.2l m/W.
Highly Efficient InGaN-based LED with Embedded Cubic Airvoids
(2014)
Lin, Da-Wei
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Huang, Jhih-Kai
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Liu, Che-Yu
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Chang, Ruey-Wen
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Wang, Sheng-Wen
Highly efficient InGaN-based LEDs with embedded sidewall passivation cubic airvoids made by nanoimprint lithography were demonstrated. The LEDs with embedded airvoids exhibit a 45% enhancement of light output at 20 mA compared with conventional LEDs.
Hole Transport Manipulation To Improve the Hole Injection for Deep Ultraviolet Light-Emitting Diodes
(2017-07-01)
Zhang, Zi-Hui
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Chen, Sung-Wen Huang
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Zhang, Yonghui
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Li, Luping
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Wang, Sheng-Wen
In this report, we propose to enhance the hole injection efficiency by adjusting the barrier height of the p-type electron blocking layer (p-EBL) for similar to 273 nm deep ultraviolet light-emitting diodes (DUV LEDs). The barrier height for the p-EBL is modified by employing a p-Al0.60Ga0.40N/Al0.50Ga0.50N/p-Al0.60Ga0.40N structure, in which the very thin Al0.50Ga0.50N layer is able to achieve a high local hole concentration, which is very effective in reducing the effective barrier height of the p-EBL for holes. More importantly, besides the thermionic emission, such a p-EBL structure can also favor a strong intraband tunneling process for holes. As a result, we can obtain a more efficient hole injection into the quantum wells, leading to a remarkably improved optical power for the DUV LED with the proposed p-EBL architecture.
Improvement of carrier distribution by using thinner quantum well with different location
(2014-01-01)
Wang, Sheng-Wen
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Lin, Da-Wei
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Lee, Chia-Yu
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Lin, Chien-Chung
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Kuo, Hao-Chung
We use thinner-quantum well to improve the droop behavior of GaN-base light emitting diode in simulation. Taking the advantage of that the thin quantum well will saturate easily, this characteristic of thin well will improve carrier distribution. Furthermore, this structure has more wave-function overlap than that of the thick well. This simulation result showed that decreasing the well thickness in specific position will not only improve the holes transport but also increase the quantum efficiency at high current density in the active region, and the efficiency droop behavior can be effectively suppressed. In this research, we designed three thin well structures by inserting different numbers of thin wells in the active region. We have compared them to the conventional LEDs, for which, the well thickness of 2.5 nm is used. The thin well structures have better droop behavior than conventional LED.
Improvement of light quality by DBR structure in white LED
(2015-02-09)
Lin, Huang-Yu
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Chen, Kuo-Ju
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Wang, Sheng-Wen
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Lin, Chien-Chung
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Wang, Kuan-Yu
This study demonstrates the application of DBR structure into the remote phosphor structure to improve the angular correlated color temperature (CCT) deviation in white light-emitting diodes (WLEDs). In the experiment, the LED device with DBR structure yielded a higher luminous efficiency than a conventional structure. The CCT deviation can be improved from 1758K to 280K in a range of -70 to 70 degree and the luminous flux increases more than 10% due to the enhancement of the light extraction of the blue light. Moreover, the reflectance of the different DBR structures is analyzed with different angles to reveal the reasons of such improvements. As the result, this LED device with DBR structure shows the great potential to use as the next generation lighting source. (C) 2014 Optical Society of America
Laser-patterned Array with Aerosol-jet Printing Quantum-dots for Novel White Light Source
(2016)
Wang, Sheng-Wen
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Lin, Huang-Yu
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Lin, Chien-Chung
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Kao, Tsung Sheng
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Chen, Kuo-Ju
Through the laser-ablation and aerosol-jet printing techniques, a novel photoluminescent quantum-dots device with microscale patterns has been demonstrated as a white-light emitting source with stable emission at different driving currents and larger color productivity domain.
Low-Temperature and Ultrafast Synthesis of Patternable Few-Layer Transition Metal Dichacogenides with Controllable Stacking Alignment by a Microwave-Assisted Selenization Process
(2016-02-23)
Chen, Yu-Ze
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Medina, Henry
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Wang, Sheng-Wen
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Su, Teng-Yu
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Li, Jian-Guang
To date, the chemical vapor deposition (CVD) process is the most popular approach because of its high yield and quality. Nevertheless, the need for a high temperature and the relatively long process time within each cycle hinder the commercial development in terms of production cost. In this work, we demonstrate a fast (<3 min) and feasible approach to synthesizing a few-layers of WSe2 and MoSe2 on arbitrary substrates by a microwave-assisted selenization process. The transition metal dichalcogenides (TMDs) can be patterned by standard photolithography. Furthermore, controllable layered growth from horizontal to vertical alignment can be achieved, leading to an enhanced chemical catalytic activity caused by large edge sites (exposed areas). As a proof, a highly sensitive NO gas sensor based on vertical WSe2 was fabricated. Moreover, our microwave assisted selenization process can be further extended to achieve other two-dimensional TMD materials because of the simplicity of the process.
Modeling Agent Self-awareness, Individual Performance and Collaborative Behavior
(2011-01-01)
Huang, Chung-Yuan
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Wang, Sheng-Wen
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Sun, Chuen-Tsai
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資訊工程學系
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Department of Computer Science
In the history of artificial intelligence (AI), primary agent focuses have been external environments, outside incentives, and behavioral responses. Internal operation mechanisms (i. e., attending to the self in the same manner as human self-awareness) have never been a concern for AI agent. Obviously, the learning concepts by which one pays attention to oneself has always been ignored by artificial intelligence researchers. However, we integrated a self-awareness mechanism into an agent's learning architecture, so that not only are an agent's thinking and behaviors closer to the ways that people operate, but also to allow agent-based social simulations to be even more akin to the real world. Our research objectives include: a) to propose a self-awareness agent model including external learning mechanism and internal cognitive capacity combining with having super-ego and ego personalities; b) apply an iterated Prisoner's Dilemma game to represent the conflicts caused by public good and private interest in an agents' society, and analyze the effects of an agent's self-awareness capacity upon its individual performance and social cooperation behavior. Our goal is to show the ability of a cognitive learning model to improve intelligent agent performance and support collaborative agent behavior. We believe additional simulations and analyses will indicate enriched social benefits, even in cases where only a few agents achieve limited self-awareness capabilities.
Modeling self-perception agents in an opinion dynamics propagation society
(2014-03-01)
Wang, Sheng-Wen
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Huang, Chung-Yuan
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Sun, Chuen-Tsai
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教育研究所
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資訊工程學系
In previous continuous opinion dynamics models based on bounded confidence assumptions, individuals can only influence each other\'s opinions when those opinions are sufficiently close; subsequently, agents construct their self-opinions using opinions collected from other agents. All of these models lack the element of an agent\'s inner self-attitude. In this paper we describe our proposal for a self-perception model in which agents are aware of differences between their attitudes and expressed opinions on specific issues. Our agents are based on a mix of self-perception and cognitive dissonance theory that allows them to self-adjust discomfort caused by inconsistencies between inner attitudes and expressed opinions. Results from a series of simulation experiments indicate that our model captures the gap between inner attitude and external opinion in explaining the private acceptance/public conformity phenomenon. We conclude with a demonstration of how our proposed model can be used in sociological studies of pluralistic ignorance.
Modeling self-perception agents in an opinion dynamics propagation society
(2014-03-01)
Wang, Sheng-Wen
;
Huang, Chung-Yuan
;
Sun, Chuen-Tsai
;
教育研究所
;
資訊工程學系
In previous continuous opinion dynamics models based on bounded confidence assumptions, individuals can only influence each other's opinions when those opinions are sufficiently close; subsequently, agents construct their self-opinions using opinions collected from other agents. All of these models lack the element of an agent's inner self-attitude. In this paper we describe our proposal for a self-perception model in which agents are aware of differences between their attitudes and expressed opinions on specific issues. Our agents are based on a mix of self-perception and cognitive dissonance theory that allows them to self-adjust discomfort caused by inconsistencies between inner attitudes and expressed opinions. Results from a series of simulation experiments indicate that our model captures the gap between inner attitude and external opinion in explaining the private acceptance/public conformity phenomenon. We conclude with a demonstration of how our proposed model can be used in sociological studies of pluralistic ignorance.
Nearly lattice-matched molybdenum disulfide/gallium nitride heterostructure enabling high-performance phototransistors
(2019-03-01)
Liu, Xinke
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Chen, Yuxuan
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Li, Dabing
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Wang, Sheng-Wen
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Ting, Chao-Cheng
Molybdenum disulfide (MoS2)-based phototransistors are attractive for optical electronics in a large-scale size, such as transparent touch screens. However, most of the work done over the past decade has been on an opaque SiO2/Si wafer with a small size (micrometer to millimeter). In this work, a large-scale multilayer MoS2-based phototransistor has been fabricated on a transparent freestanding gallium nitride (GaN) wafer using a scalable chemical vapor deposition method. Due to the near lattice match and small thermal expansion mismatch between GaN and MoS2, the as-grown multilayer MoS2-on-GaN film shows high material quality in terms of low full width at half-maximum (similar to 5.16 cm(-1)) for the E-2g(1) Raman mode and a high absorption coefficient (similar to 10(6) cm(-1)) in the wavelength range of 405-638 nm. Under a wavelength of 405 nm at an incident power of 2 mWand applied voltage of 9 V, the fabricated MoS2-on-GaN phototransistor achieved a maximum responsivity of 17.2 A/W, a photocurrent gain of 53.6, and an external quantum efficiency of 5289%, with specific detectivity (similar to 10(10)-10(12) Jones) and low noise equivalent power (10(-12)-10(-14) W/Hz(1/2)) in the visible range of 405-638 nm. A typical response time of 0.1-4 s in the ambient air has also been recorded for the demonstrated MoS2-on-GaN phototransistor. Our work paves a technologic stepping stone for MoS2-based phototransistors for multifunctional transparent and touch-based optoelectronics in the future. (C) 2019 Chinese Laser Press
Phase-Engineered PtSe2-Layered Films by a Plasma-Assisted Selenization Process toward All PtSe2-Based Field Effect Transistor to Highly Sensitive, Flexible, and Wide-Spectrum Photoresponse Photodetectors
(2018-05-09)
Su, Teng-Yu
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Medina, Henry
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Chen, Yu-Ze
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Wang, Sheng-Wen
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Lee, Shao-Shin
The formation of PtSe2-layered films is reported in a large area by the direct plasma-assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 degrees C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe2-layered film (five monolayers) exhibits a metallic behavior. A clear p-type semiconducting behavior of the PtSe2-layered film (approximate to trilayers) is observed with the average field effective mobility of 0.7 cm(2) V-1 s(-1) from back-gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe2 field effect transistor is demonstrated where the thinner PtSe2, exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe2, exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe2-layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 mu A under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.