Browsing by Author "Chen, Yu-Tzu"

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Design and Fabrication of the Reliable GaN Based Vertical-Cavity Surface-Emitting Laser via Tunnel Junction
(2019-04-01)
Shen, Chih-Chiang
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Lu, Yun-Ting
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Yeh, Yen-Wei
;
Chen, Cheng-Yuan
;
Chen, Yu-Tzu
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of the VCSEL with TJ structure was much smaller than that of the VCSEL with an Indium-Tin-Oxide (ITO) layer. We have been demonstrated that laser output performance is improved by using the TJ structure when compared to the typical VCSEL structure of the ITO layer. The output power obtained at 2.1 mW was enhanced by a factor of 3.5 by the successful reduction of threshold current density (J(th)) from 12 to 8.5 kA/cm(2), and the enlarged slope efficiency was due to less absorption in VCSEL with a TJ structure. Finally, the samples passed the high temperature (70 degrees C) and high operation current (1.5 x J(th)) test for over 500 h.
Design, Modeling, and Fabrication of High-Speed VCSEL with Data Rate up to 50 Gb/s
(2019-08-14)
Shen, Chih-Chiang
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Hsu, Tsung-Chi
;
Yeh, Yen-Wei
;
Kang, Chieh-Yu
;
Lu, Yun-Ting
We have studied the characteristics of frequency response at 850-nm GaAs high-speed vertical-cavity surface-emitting lasers (VCSELs) with different kinds of oxide aperture sizes and cavity length using the PICS3D simulation program. Using 5-mu m oxide aperture sizes, the frequency response behavior can be improved from 18.4 GHz and 15.5 GHz to 21.2 GHz and 19 GHz in a maximum of 3 dB at 25 degrees C and 85 degrees C, respectively. Numerical simulation results also suggest that the frequency response performances improved from 21.2 GHz and 19 GHz to 30.5 GHz and 24.5 GHz in a maximum of 3 dB at 25 degrees C and 85 degrees C due to the reduction of cavity length from 3 lambda/2 to lambda/2. Consequently, the high-speed VCSEL devices were fabricated on a modified structure and exhibited 50-Gb/s data rate at 85 degrees C.
First exit from an open set for a matrix-exponential Levy process
(2017-08-01)
Chen, Yu-Ting
;
Chen, Yu-Tzu
;
Sheu, Yuan-Chung
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應用數學系
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Department of Applied Mathematics
We study the first exit from a general open set for a one-dimensional Levy process, where the Levy measure is proportional to a two-sided matrix-exponential distribution. Under appropriate conditions on the Levy measure, we obtain an explicit solution for the joint distribution of the first-exit time and the position of the Levy process upon first exit, in terms of the zeros and poles of the corresponding Laplace exponent. The present result complements several earlier works on the use of exit sets for Levy processes with algebraically similar Laplace exponents, where exits from open intervals are the main focus. Published by Elsevier B.V.
Ultrathin single-crystalline silicon solar cells for mechanically flexible and optimal surface morphology designs
(2015-09-01)
Lin, Ching-Chang
;
Chuang, Yi-Jiun
;
Sun, Wen-Hsien
;
Cheng, Chieh
;
Chen, Yu-Tzu
Recently, the evolution of photovoltaic cells in together with flexible electronics rapidly grows up so as to satisfy the flexibility and elasticity needs. Therefore, it will be a breakthrough impact if it is able to develop flexible single-crystalline photovoltaic cells which are fabricated with traditional procedure and provide highly electrical properties as well. This study aims to fabricate the flexible solar photovoltaic device with practical and reproducible method. Generally, the flexible solar photovoltaic is manufactured on the 30 gm-thickness single-crystalline silicon chip by chemical etching process. Versatile design on the flexible device can enhance light trapping effect. The surface texturization and antireflection layer deposition successfully minimize the reflectivity losses from the incident light. In addition, the developed devices under concave bending morphology demonstrates better operating performance than convex and flat configurations. As to the concave bending type, the significant improvement of power conversion efficiency (129% better than flat type, and 161% better than convex type) is observed from a large device current, which is related to the contribution of light trapping enhancement. In combination of all optimal conditions, the flexible device exhibits conversion efficiency up to 13.8%. The development of novel flexible solar photovoltaics with the excellent mechanical flexibility, low silicon material consumption and low fabrication cost demonstrates the potential capability for future solar cells. (C) 2015 Elsevier B.V. All rights reserved.