Browsing by Author "Chen, Sung-Wen Huang"

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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.
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.
Analysis of the back-barrier effect in AlGaN/GaN high electron mobility transistor on free-standing GaN substrates
(2020-01-25)
Liu, Xinke
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Wang, Hao-Yu
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Chiu, Hsien-Chin
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Chen, Yuxuan
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Li, Dabing
The effect of AlGaN back-barrier on AlGaN/GaN high electron mobility transistors (HEMTs) using freestanding GaN wafer has been investigated in this work. With the introducing back-barrier structure, the leakage path underneath the buffer (native nitrogen-vacancies and GaOx compounds of the HVPE-grown free-standing GaN surface) layer can be suppressed by lift-up the conduction band. As compared with AlGaN/GaN HEMTs on SiC wafer, AlGaN/GaN HEMTs on free-standing GaN wafer show enhanced drain current ( 700 mA/mm), improved transconductance (143 mS/mm), less current collapse (12%), higher current gain cut-off frequency (13 GHz), and maximum stable gain cut-off frequency (24 GHz), which is attributed to the higher epi quality layer on free-standing GaN wafer. (C) 2019 Elsevier B.V. All rights reserved.
Assessment and Optimization of the Circadian Performance of Smartphone-Based Virtual Reality Displays
(2019-01-01)
Wu, Tingzhu
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Liang, Shijie
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Zheng, Lili
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Lin, Yue
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Guo, Ziquan
The non-visual effects of blue light in displays mean that excessive use of smartphones can disturb the human circadian rhythm. Thus, the impact of virtual reality (VR) headsets, which are worn closer to the human eye, may be even more serious. In this paper, based on non-visual parameters, such as the circadian action factor (CAF) and circadian illuminance, the circadian performance of smartphone-based VR displays is quantitatively evaluated by an evaluation system we designed. Moreover, we investigate the improvements in the circadian performance of VR headsets resulting from three practical methods for reducing the blue light content. Finally, a theoretical method of shifting the green-light wavelength of the screen close to 555 nm to optimize the CAF of VR headsets is proposed. Overall, the results of this paper are of significant value in quantifying the effects of VR displays on circadian rhythms and improving the safety of VR headsets with regard to human health.
Design Strategies for Mesa-Type GaN-Based Schottky Barrier Diodes for Obtaining High Breakdown Voltage and Low Leakage Current
(2020-05-01)
Jia, Xingyu
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Chen, Sung-Wen Huang
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Liu, Yajin
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Hou, Xu
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Zhang, Yonghui
In this article, we have systematically investigated the impact of different structural parameters on the breakdown voltage for GaN-based trench MIS barrier-controlled Schottky (TMBS) rectifier. Compared with the planar Schottky rectifier, the TMBS rectifier has field plates on the mesa sidewalls so that the drift region can be depleted in a 2-D manner, which helps to decrease the electric field at the metal/mesa interface. However, the adoption of mesas can make the electric potential lines at the mesa corner dense and has large curvatures. Therefore, the premature breakdown can occur when the electric field therein reaches the critical condition. We find that the electric field profiles can be affected by insulation layer thickness, mesa width, trench depth, and different types of insulation layers. Then, we increase the breakdown voltage by homogenizing the electric field distribution in the mesa region, e.g., the electric field at mesa corners can be decreased by adopting properly thick sidewall insulator and small trench depth. Meanwhile, TMBS rectifier using sidewall insulating material with a large dielectric constant more favors a large breakdown voltage.
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.
Full-color micro-LED display with high color stability using semipolar (20-21) InGaN LEDs and quantum-dot photoresist
(2020-05-01)
Chen, Sung-Wen Huang
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Huang, Yu-Ming
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Singh, Konthoujam James
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Hsu, Yu-Chien
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Liou, Fang-Jyun
Red-green-blue (RGB) full-color micro light-emitting diodes (mu-LEDs) fabricated from semipolar (20-21) wafers, with a quantum-dot photoresist color-conversion layer, were demonstrated. The semipolar (20-21) InGaN/GaN mu-LEDs were fabricated on large (4 in.) patterned sapphire substrates by orientation-controlled epitaxy. The semipolar mu-LEDs showed a 3.2 nm peak wavelength shift and a 14.7% efficiency droop under 200 A/cm(2 )injected current density, indicating significant amelioration of the quantum-confined Stark effect. Because of the semipolar mu-LEDs' emission-wavelength stability, the RGB pixel showed little color shift with current density and achieved a wide color gamut (114.4% NTSC space and 85.4% Rec. 2020). (C) 2020 Chinese Laser Press
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
High-Bandwidth Green Semipolar (20-21) InGaN/GaN Micro Light-Emitting Diodes for Visible Light Communication
(2020-08-19)
Chen, Sung-Wen Huang
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Huang, Yu-Ming
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Chang, Yun-Han
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Lin, Yue
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Liou, Fang-Jyun
The light-emitting diode (LED) is among promising candidates of light sources in visible light communication (VLC); however, strong internal polarization fields in common c-plane LEDs, especially green LEDs, result in low frequency and limited transmission performance. This study aims to overcome the limited 3-dB bandwidth of long-wavelength InGaN/GaN LEDs. Thus, semipolar (20-21) micro-LEDs (mu LEDs) were fabricated through several improved approaches on epitaxy and chip processes. The mu LED exhibits a 525 nm peak wavelength and good polarization performance. The highest 3-dB bandwidth up to 756 MHz and 1.5 Gbit/s data rate was achieved under a current density of 2.0 kA/cm(2). These results suggest a good transmission capacity of green semipolar (20-21) mu LEDs in VLC applications.
Highly Efficient and Stable White Light-Emitting Diodes Using Perovskite Quantum Dot Paper
(1970-01-01)
Kong, Chieh-Yu
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Lin, Chun-Ho
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Lin, Chih-Hao
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Li, Ting-You
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Chen, Sung-Wen Huang
Perovskite quantum dots (PQDs) are a competitive candidate for next-generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD-based white light-emitting diodes (LEDs) show only modest luminous efficiency of approximate to 50 lm W-1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4(+) phosphor and blue GaN LED chips to fabricate a high-performance white LED demonstrating ultrahigh luminous efficiency (124 lm W-1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.
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.
Increasing the hole energy by grading the alloy composition of the p-type electron blocking layer for very high-performance deep ultraviolet light-emitting diodes
(2019-04-01)
Zhang, Zi-Hui
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Kou, Jianquan
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Chen, Sung-Wen Huang
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Shao, Hua
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Che, Jiamang
It is well known that the p-type AlGaN electron blocking layer (p-EBL) can block hole injection for deep ultraviolet light-emitting diodes (DUV LEDs). The polarization induced electric field in the p-EBL for [0001] oriented DUV LEDs makes the holes less mobile and thus further decreases the hole injection capability. Fortunately, enhanced hole injection is doable by making holes lose less energy, and this is enabled by a specifically designed p-EBL structure that has a graded MN composition. The proposed p-EEL can screen the polarization induced electric field in the p-EBL. As a result, holes will lose less energy after going through the proposed p-EBL, which correspondingly leads to the enhanced hole injection. Thus, an external quantum efficiency of 7.6% for the 275 nm DIN LED structure is obtained. (C) 2019 Chinese Laser Press
Interplay of carriers and deep-level recombination centers of 275-nm light-emitting diodes - Analysis on the parasitic peaks over wide ranges of temperature and injection density
(2019-08-05)
Wu, Tingzhu
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Lin, Yue
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Peng, Zhangbao
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Chen, Huashan
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Shangguan, Zhibin
The low luminance efficiency, poor reliability and parasitic peaks have greatly limited the commercialization of deep ultraviolet (DUV) light-emitting diodes. Tasks of identifying the culprits of these deficits are of paramount importance but remains unaccomplished. We employ the full-range temperature (20 K - 300 K) measurement on 275-nm DUV devices that subjected to a 15-hour current-stress aging. The results suggest that the primary culprit of fast luminous decay is the proliferation of non-radiative centers. The origins of two main parasitic peaks are identified. The 310-nm peak is considered to solely come from deep-level radiative centers (DLRCs) that only dwell in the active region. Whereas, the 400-nm peak is proven to be dual-sources. One is related to the DLRCs in the active region, which only can be observed at very low currents; the other emerging at higher currents are associated with similar kinds of DLRCs located in the p-region, which only are excited when electrons overflow. This new discovery also demonstrates that a thorough investigation on the interplay among carriers and various types of defects should be conducted on the basis of the measurement that is taken under a wide temperature range, as well as under a proper forward voltage. This is to let the quasi-Fermi level shift across deep defect levels, the band-edge, and to over-band, whereby these recombination sites are exposed to deficit, moderate and saturated electron environment so that their natures can be well tested. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology
(2018-09-01)
Wu, Tingzhu
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Sher, Chin-Wei
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Lin, Yue
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Lee, Chun-Fu
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Liang, Shijie
Displays based on inorganic light-emitting diodes (LED) are considered as the most promising one among the display technologies for the next-generation. The chip for LED display bears similar features to those currently in use for general lighting, but it size is shrunk to below 200 microns. Thus, the advantages of high efficiency and long life span of conventional LED chips are inherited by miniaturized ones. As the size gets smaller, the resolution enhances, but at the expense of elevating the complexity of fabrication. In this review, we introduce two sorts of inorganic LED displays, namely relatively large and small varieties. The mini-LEDs with chip sizes ranging from 100 to 200 m have already been commercialized for backlight sources in consumer electronics applications. The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions. The micro-LEDs with chip size less than 100 m, still remain in the laboratory. The full-color solution, one of the key technologies along with its three main components, red, green, and blue chips, as well color conversion, and optical lens synthesis, are introduced in detail. Moreover, this review provides an account for contemporary technologies as well as a clear view of inorganic and miniaturized LED displays for the display community.
Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency
(2018-04-24)
Zhang, Zi-Hui
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Chen, Sung-Wen Huang
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Chu, Chunshuang
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Tian, Kangkai
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Fang, Mengqian
This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally.
On the Carrier Transport for InGaN/GaN Core-Shell Nanorod Green Light-Emitting Diodes
(2019-01-01)
Kou, Jianquan
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Chen, Sung-Wen Huang
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Che, Jiamang
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Shao, Hua
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Chu, Chunshuang
In this paper, we model and investigate the carrier transport for the core-shell nanorod (NR) structured green light-emitting diodes (LEDs) for which the InGaN/GaN multiple quantum wells are grown on the nonpolar surface of the NR. Our results show the absence of polarization fields in the m-plane quantum wells for the core-shell NR LEDs, which manifest the flat energy band condition, the improved electron injection efficiency, and the high electron-hole wave functions overlap for the quantum wells, leading to the high radiative recombination rate and the enhanced quantum efficiency. We further find that the quantum efficiency is also affected by the vertical charge injection for the core-shell NR LEDs. The vertical charge injection is more sensitive to the doping concentration and the thickness of the p-GaN layer than of the n-GaN layer. Moreover, the increase of the NR height also leads to the nonuniform vertical charge injection.
Vertical GaN-on-GaN PIN diodes fabricated on free-standing GaN wafer using an ammonothermal method
(2019-10-05)
Chen, Sung-Wen Huang
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Wang, Hao-Yu
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Hu, Cong
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Chen, Yong
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Wang, Hao
We report vertical GaN-on-GaN PIN diodes with a record high figure-of-merit (V-BR(2)/R-on) of 29.7 GW/cm(2) on free-standing GaN wafer using a complementary metal-oxide-semiconductor (CMOS) compatible contact materials. Due to the low substrate resistivity, low contact resistance, and high quality of GaN drift layer, a low on-state resistance R(on )of 0.31 m Omega cm(2) is obtained. With integrating of the metal filed plate structure in the vertical device, the peak electrical field along the GaN mesa edge can be significantly reduced, thus leading to a high breakdown voltage V-BR of 3.04 kV. The vertical GaN-on-GaN PIN diodes in this work show turn-on voltage V-on of similar to 3.4 V, on/off current ratio of similar to 1.3 x 10(7), and ideal factor n of similar to 2.2. According to the reverse switching measurement, the reverse recovery time T-rr. (reverse recovery charge Q(rr)) is 22.8 ns (4.8 nC) and 24.0 ns (5.4 nC), respectively, under a testing temperature of 300 K and 500 K. (C) 2019 Elsevier B.V. All rights reserved.
Wavelength Tuning in InGaN/GaN Light-emitting Diodes with Strain-induced Through Nanosphere Lithography
(2017-01-01)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Tsai, Yu-Lin
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Tzou, An-Jye
Nano-ring light emitting diodes with different wall width shows that the effective bandgap can be tuned by reducing the strain. This research successful to make the devices with four colors emission on the same wafer.