Browsing by Author "Kuo, Hao Chung"

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A Bilayer 2D-WS2/Organic-Based Heterojunction for High-Performance Photodetectors
(2019-09-01)
Huang, Feng
;
Li, Jing Zhou
;
Xu, Zhu Hua
;
Liu, Yuan
;
Luo, Ri Peng
Two-dimensional (2D) tungsten disulfide (WS2) has inspired great efforts in optoelectronics, such as in solar cells, light-emitting diodes, and photodetectors. However, chemical vapor deposition (CVD) grown 2D WS2 domains with the coexistence of a discontinuous single layer and multilayers are still not suitable for the fabrication of photodetectors on a large scale. An emerging field in the integration of organic materials with 2D materials offers the advantages of molecular diversity and flexibility to provide an exciting aspect on high-performance device applications. Herein, we fabricated a photodetector based on a 2D-WS2/organic semiconductor materials (mixture of the (Poly-(N,N '-bis-4-butylphenyl-N,N '-bisphenyl) benzidine and Phenyl-C61-butyric acid methyl ester (Poly-TPD/PCBM)) heterojunction. The application of Poly-TPD/PCBM organic blend film enhanced light absorption, electrically connected the isolated WS2 domains, and promoted the separation of electron-hole pairs. The generated exciton could sufficiently diffuse to the interface of the WS2 and the organic blend layers for efficient charge separation, where Poly-TPD was favorable for hole carrier transport and PCBM for electron transport to their respective electrodes. We show that the photodetector exhibited high responsivity, detectivity, and an on/off ratio of 0.1 A/W, 1.1 x 10(11) Jones, and 100, respectively. In addition, the photodetector showed a broad spectral response from 500 nm to 750 nm, with a peak external quantum efficiency (EQE) of 8%. Our work offers a facile solution-coating process combined with a CVD technique to prepare an inorganic/organic heterojunction photodetector with high performance on silicon substrate.
A novel randomly textured phosphor structure for highly efficient white light-emitting diodes
(2012-03-16)
Chen, Hsin Chu
;
Chen, Kuo Ju
;
Wang, Chao Hsun
;
Lin, Chien Chung
;
Yeh, Chia Chi
We have successfully demonstrated the enhanced luminous flux and lumen efficiency in white light-emitting diodes by the randomly textured phosphor structure. The textured phosphor structure was fabricated by a simple imprinting technique, which does not need an expensive dry-etching machine or a complex patterned definition. The textured phosphor structure increases luminous flux by 5.4% and 2.5% at a driving current of 120 mA, compared with the flat phosphor and half-spherical lens structures, respectively. The increment was due to the scattering of textured surface and also the phosphor particles, leading to the enhancement of utilization efficiency of blue light. Furthermore, the textured phosphor structure has a larger view angle at the full width at half maximum (87A degrees) than the reference LEDs.
Effects of Inhomogeneous Gain and Loss on Nitride-Based Vertical-Cavity Surface Emitting Lasers
(2009-04-01)
Chen, Shih Wei
;
Lo, Ming Hua
;
Kao, Tsung Ting
;
Kao, Chih Chiang
;
Chu, Jung Tang
Nitride-based vertical cavity surface emitting lasers (VCSEL) with hybrid mirror has been investigated. We further measured the as-grown samples (without top dielectric distributed Bragg reflector) by p-photoluminescence, scanning near-field optical microscopy, and cathodoluminescence (CL). By different excitation power density, the experimental results indicated that the VCSEL devices have different lasing modes and spot sizes, represented inhomogeneous gain and loss distribution in the whole structure. The non-uniform emission intensity distribution including several bright spots of about 1 to 2 pm was observed for both VCSEL devices and as-grown samples, which was obtained from CL measurement, due to the effect of indium clusters and non-uniform micro-cavity resonant in InGaN multi-quantum wells (MQWs). The results show the significant influence on commercial applications such as light emitting diodes, lasers devices and so on. (C) 2009 The Japan Society of Applied Physics
Efficiency Enhancement InGaP/GaAs Dual-Junction Solar Cell with Subwavelength Antireflection Nanorod Arrays
(2011-12-01)
Tsai, Min-An
;
Chen, Hsin Chu
;
Tseng, Ping Chen
;
Yu, Peichen
;
Chiu, Chin Hua
The enhanced conversion efficiency of the InGaP/GaAs dual-junction solar cell was demonstrated utilizing broad-band and omnidirectional antireflection nanorod arrays. The nanorod arrays were fabricated by self-assembled Ni clusters, followed by inductively-coupled-plasma reactive ion etching. The conversion efficiency measured under one-sun air mass 1.5 global illuminations at room temperature was improved by 10.8%. The light absorption efficiencies of the top InGaP and bottom GaAs cells were also studied under the influence of nanorod arrays. The enhanced absorption efficiency was mostly contributed from the short wavelength absorption by top cell. Surface nanorod arrays served not only as broad-band omnidirectional antireflection layers but also scattering sources. The structure can be further optimized to obtain the maximum conversion efficiency.
Enhanced performance of nitride-based ultraviolet vertical-injection light-emitting diodes by non-insulation current blocking layer and textured surface
(2014-12-29)
Chiang, Yen Chih
;
Lin, Bing Cheng
;
Chen, Kuo Ju
;
Lin, Chien Chung
;
Lee, Po Tsung
For the purpose of light extraction and efficiency enhancement, the nitride-based ultraviolet vertical-injection light-emitting diodes (UV-VLEDs) with non-insulation current blocking layer (n-CBL) and optimized textured surface were fabricated. The optical and electrical characteristics were investigated in this n-CBL UV-VLED. Furthermore, the efficiency of optimized structure was improved by 5 similar to 6 times compared to our reference.
High-efficiency and low assembly-dependent chip-scale package for white light-emitting diodes
(2015-04-21)
Huang, Che-Hsuan
;
Chen, Kuo-Ju
;
Tsai, Ming-Ta
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Shih, Min-Hsiung
;
Sun, Chia-Wei
This article presents a chip-scale package (CSP) with conformal and uniform structures for white light-emitting diodes used in lighting and backlight unit (BLU) applications. The CSP structures produce higher light extraction efficiency and lower assembly-dependent packaging compared with conventional surface-mounted devices (SMDs). Simulation results show that compared with SMDs, the luminous efficiency of CSP structures is 8.81% higher in lighting applications and 9.43% higher in BLU applications. This is likely due to light loss in the light bowl of the SMDs. Moreover, CSPs with a conformal phosphor structure exhibit low assembly dependence and redundancy, and rb-CSPs with a conformal structure are a more effective light source in both lighting and BLU applications. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Investigation of the Impact of Drive Current and Phosphor Thickness on the Reliability of High Power White LED Lamp
(2019-06-01)
Singh, Preetpal
;
Tan, Cher Ming
;
Zhao, Wenyu
;
Kuo, Hao Chung
;
交大名義發表
Lumen flux of white light-emitting diodes (LEDs) can be increased by increasing phosphor layer thickness and blue LED's drive current. Higher LED currents will lead to an increase in blue light in the output lumen along with higher temperatures which is not acceptable, and a corresponding decrease in the yellow light emission. The physical reason for this decrease is attributed to the finite phosphor particles in the layer and re-emission occurring due to scattered or back reflected blue light rays. A parameter called blue to yellow ratio (BYR) is used which can lead to a current with maximum phosphor utilization while preventing the LED output color to shift from white toward blue. As the degree of impact on reliability from drive current and thickness is different, a careful adjustment of the drive current and phosphor layer thickness shall be made for a given lumen. Response surface method is employed to obtain an optimal combination of the current and thickness where the temperature is the minimum for a given lumen level. The temperature difference for different combinations of current and thickness for a given lumen can be as high as 15 degrees C as found in this paper.
Novel thin-GaN LED structure adopted micro abraded surface to compare with conventional vertical LEDs in ultraviolet light
(2015-04-15)
Chiang, Yen Chih
;
Lin, Chien Chung
;
Kuo, Hao Chung
;
光電系統研究所
;
照明與能源光電研究所
In this study, novel thin-GaN-based ultraviolet light-emitting diodes (NTG-LEDs) were fabricated using wafer bonding, laser lift-off, dry etching, textured surface, and interconnection techniques. Placing PN electrodes on the same side minimized the absorption caused by electrodes in conventional vertical injection light-emitting diodes (V-LEDs) and the current spreading was improved. The light output power (700 mA) of the NTG-LEDs was enhanced by 18.3% compared with that of the V-LEDs, and the external quantum efficiency (EQE) of the NTG-LEDs was also relatively enhanced by 20.0% compared with that of a reference device. When the current operations were 1,500 mA, the enhancements of the light output power and EQE were 27.4% and 27.2%, respectively. Additionally, the efficiency droop was improved by more than 15% at the same current level.
Recombination Pathways in Green InGaN/GaN Multiple Quantum Wells
(2017-02-21)
Lin, Tao
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Kuo, Hao Chung
;
Jiang, Xiao Dong
;
Feng, Zhe Chuan
;
光電工程學系
This paper reports the transient photoluminescence (PL) properties of an InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) with green emission. Recombination of localized excitons was proved to be the main microscopic mechanism of green emission in the sample. The PL dynamics were ascribed to two pathways of the exciton recombination, corresponding to the fast decay and the slow decay, respectively. The origins of slow decay and fast decay were assigned to local compositional fluctuations of indium and thickness variations of InGaN layers, respectively. Furthermore, the contributions of two decay pathways to the green PL were found to vary at different emission photon energy. The fraction of fast decay pathway decreased with decreasing photon energy. The slow radiative PL from deep localized exciton recombination suffered less suppression from non-radiative delocalization process, for the higher requested activation energy. All these results supported a clear microscopy mechanism of excitation-emission process of the green MQW LED structure.