Browsing by Author "Shen, Chih-Chiang"

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850/940-nm VCSEL for optical communication and 3D sensing
(2018-01-01)
Cheng, Chih-Hsien
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Shen, Chih-Chiang
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Kao, Hsuan-Yun
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Hsieh, Dan-Hua
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Wang, Huai-Yung
This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.
A critical review on two-dimensional quantum dots (2D QDs): From synthesis toward applications in energy and optoelectronics
(2019-11-01)
Manikandan, Arumugam
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Chen, Yu-Ze
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Shen, Chih-Chiang
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Sher, Chin-Wei
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Kuo, Hao-Chung
Recent advances in the development of quantum dots (QDs) have offered new possibilities for the exploration of sensors, bio imaging, batteries, electrochemical water splitting and optoelectronic applications because of their intriguing optical, electrical, catalytic and electrochemical properties. Among QDs, atomically thin two-dimensional quantum dots (2D QDs) derived from graphene sheets, transition metal dichalcogenide (TMD) layers and phosphorene have been of considerable interest for the past few years. There have been several intensive studies of carbon QDs, but TMD QDs and heterostructures based on 2D QDs are rapidly advancing. Herein, the synthesis and properties of 2D QDs, particularly carbon and TMD QDs, are reviewed for the recent progress in their application toward electrochemical water splitting, photocatalytic wastewater treatment, supercapacitors, batteries and photodetectors. Moreover, the assembly of such 2D QDs to achieve industrial-scale production and boost their performance in widespread applications is emphasized.
Deep-ultraviolet Raman scattering studies of monolayer graphene thin films
(2015-01-01)
Liu, Hsiang-Lin
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Siregar, Syahril
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Hasdeo, Eddwi H.
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Kumamoto, Yasuaki
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Shen, Chih-Chiang
We present joint experimental and theoretical investigations of the deep-ultraviolet Raman scattering spectra of monolayer graphene thin films. We found that upon a 266 nm laser excitation, while the G mode remains pronounced, the G\' mode is not observed. The G\' mode exhibits distinctive linewidth broadening towards the ultraviolet frequency region. The peak intensity ratio of the G\' and G modes increases dramatically excited at 355, 532, and 785 nm wavelengths. All of the experimental findings are in good agreement with the theory calculated by the tight-binding method. We theoretically show that the integrated intensity of the G\' mode is inversely proportional to the incident photon energy, whereas that of the G mode increases as the fourth power of the incident photon energy. These results extend our understanding of the double resonance Raman scattering process of graphene away from the Dirac cones and provide the foundation for future technologically important developments of graphene in the deep-ultraviolet frequency range. (C) 2014 Elsevier Ltd. All rights reserved.
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
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Chen, Cheng-Yuan
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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
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Yeh, Yen-Wei
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Kang, Chieh-Yu
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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.
Full-color monolithic hybrid quantum dot nanoring micro light-emitting diodes with improved efficiency using atomic layer deposition and nonradiative resonant energy transfer
(2019-04-01)
Chen, Sung-Wen Huang
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Shen, Chih-Chiang
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Wu, Tingzhu
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Liao, Zhen-You
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Chen, Lee-Feng
Full-color displays based on micro light-emitting diodes (mu LEDs) can be fabricated on monolithic epitaxial wafers. Nanoring (NR) structures were fabricated on a green LED epitaxial wafer; the color of NR-mu LEDs was tuned from green to blue through strain relaxation. An Al2O3 layer was deposited on the sidewall of NR-mu LEDs, which improved the photoluminescence intensity by 143.7%. Coupling with the exposed multiple quantum wells through nonradiative resonant energy transfer, red quantum dots were printed to NR-mu LEDs for a full-color display. To further improve the color purity of the red light, a distributed Bragg reflector is developed to reuse the excitation light. (C) 2019 Chinese Laser Press
Impact of the surface recombination on InGaN/GaN-based blue micro-light emitting diodes
(2019-06-10)
Kou, Jianquan
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Shen, Chih-Chiang
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Shao, Hua
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Che, Jiamang
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Hou, Xu
In this work, the size-dependent effect for InGaN/GaN-based blue micro-light emitting diodes (mu LEDs) is numerically investigated. Our results show that the external quantum efficiency (EQE) and the optical power density drop drastically as the device size decreases when sidewall defects are induced. The observations are owing to the higher surface-to-volume ratio for small mu LEDs, which makes the Shockley-Read-Hall (SRH) non-radiative recombination at the sidewall defects not negligible. The sidewall defects also severely affect the injection capability for electrons and holes, such that the electrons and holes are captured by sidewall defects for the SRH recombination. Thus, the poor carrier injection shall be deemed as a challenge for achieving high-brightness mu LEDs. Our studies also indicate that the sidewall defects form current leakage channels, and this is reflected by the current density-voltage characteristics. However, the improved current spreading effect can be obtained when the chip size decreases. The better current spreading effect takes account for the reduced forward voltage. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Observation of Femtosecond Acoustic Anomaly in a Solid Liquid Interface
(2020-02-06)
Sun, Chi-Kuang
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Yao, Yi-Ting
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Shen, Chih-Chiang
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Ho, Mu-Han
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Lu, Tien-Chang
Here we report a femtosecond anomaly observed at a solid liquid interface: femtosecond acoustic echo being advanced by the application of a viscous liquid to the solid surface. Through extensive simulation and experiments, we attribute this new discovery to the effect introduced by the surface-adsorbed water layer, switching between properties more viscous than water and more solid-like than ice. Our study further indicates a new technology paradigm: the femtosecond acoustic system to probe the viscoelastic properties of the surface-adsorbed water layer, which is not achievable by any available current technology.