Browsing by Author "Lin, Da-Wei"

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A Study of Mechanical Lift-Off Technology for High-Efficiency Vertical LEDs Using Micro-Porous GaN Template
(2013-01-01)
Lee, Chia-Yu
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Lin, Da-Wei
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Liu, Che-Yu
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Hsu, Shih-Chieh
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Kuo, Hao-Chung
The high efficiency vertical light emitting diodes (V-LEDs) using mechanical lift-off with Micro-Porous GaN template formed by high temperature molten KOH wet etching process were demonstrated. The average threading dislocation density (TDD) of u-GaN after regrowth was estimated by transmission electron microscopy (TEM) reduced from 2x10(9) to 1x10(8) cm(2). The sapphire substrate was easily removed by mechanical lift-off during wafer bonding process. The light output of V-LEDs are greatly enhanced by 100% compared with Conventional-LEDs at an operating current of 20mA due to the high quality thin GaN and excellent heating dissipation.
A ZnO/InN/GaN Heterojunction Photodetector with Extended Infrared Response
(2015)
Hsu, Lung-Hsing
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Hsu, Shun-Chieh
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Lee, Hsin-Ying
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Tsai, Yu-Lin
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Lin, Da-Wei
An extended infrared photoresponse is observed in a ZnO/InN/GaN heterojunction diode with InN grown by MOCVD. The external quantum efficiency is measured between 1200 and 1800 nm and can be as high as 3.55%.
Blue resonant-cavity light-emitting diode with half milliwatt output power
(2016-01-01)
Yeh, Pinghui S.
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Chang, Chi-Chieh
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Chen, Yu-Ting
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Lin, Da-Wei
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Wu, Chun Chia
GaN-based resonant-cavity light-emitting diode (RCLED) has a circular output beam with superior directionality than conventional LED and has power scalability by using two-dimensional-array layout. In this work, blue RCLEDs with a top reflector of approximately 50% reflectance were fabricated and characterized. An output power of more than 0.5 mW per diode was achieved before packaging under room-temperature continuous-wave (CW) operation. The full width at half maximum (FWHM) of the emission spectrum was approximately 3.5 and 4.5 nm for 10- and 20-mu m-diameter devices, respectively. And the peak wavelength as well as the FWHM remained stable at various currents and temperatures.
Bridging the "green gap" of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals
(2016-01-01)
Tsai, Yu-Lin
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Liu, Che-Yu
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Krishnan, Chirenjeevi
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Lin, Da-Wei
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Chu, You-Chen
Green LEDs do not show the same level of performance as their blue and red cousins, greatly hindering the solid-state lighting development, which is the so-called "green gap". In this work, nano-void photonic crystals (NVPCs) were fabricated to embed within the GaN/InGaN green LEDs by using epitaxial lateral overgrowth (ELO) and nano-sphere lithography techniques. The NVPCs act as an efficient scattering back-reflector to outcouple the guided and downward photons, which not only boost the light extraction efficiency of LEDs with an enhancement of 78% but also collimate the view angle of LEDs from 131.5 degrees to 114.0 degrees. This could be because of the highly scattering nature of NVPCs which reduce the interference giving rise to Fabry-Perot resonance. Moreover, due to the threading dislocation suppression and strain relief by the NVPCs, the internal quantum efficiency was increased by 25% and droop behavior was reduced from 37.4% to 25.9%. The enhancement of light output power can be achieved as high as 151% at a driving current of 350 mA. Giant light output enhancement and directional control via NVPCs point the way towards a promising avenue of solid-state lighting.
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.
Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks
(2012-12-03)
Lin, Da-Wei
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Lee, Chia-Yu
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Liu, Che-Yu
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Han, Hau-Vei
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Lan, Yu-Pin
This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal-organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768950]
Efficiency and droop improvement in InGaN/GaN light-emitting diodes by selectively carrier-distribution manipulation
(2012)
Lin, Da-Wei
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Wang, Chao-Hsun
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Chang, Shih-Pang
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Ku, Pu-Hsih
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Lan, Yu-Pin
Efficiency and droop behavior in InGaN/GaN light-emitting diodes are both improved by selectively-graded-composition multi-quantum barriers (SGQB). Simulation results show that SGQB could moderately improve the hole transport in active region. In the meantime, spatial distribution overlap between electrons and holes in active region could be also well-considered. Therefore, the radiative recombination of SGQB LED is more efficient than that of conventional LED. The overall efficiency and droop behavior are simultaneously improved in SGQB LED, at both low and high current density.
Efficiency droop behavior improvement through barrier thickness modification for GaN-on-silicon light-emitting diodes
(2015-03-05)
Tzou, An-Jye
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Lin, Bing-Cheng
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Lee, Chia-Yu
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Lin, Da-Wei
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Liao, Yu-Kuang
Crack-free GaN-based light-emitting diodes (LEDs) were grown on 150-mm-diameter Si substrates by using low-pressure metal-organic chemical vapor deposition. The relationship between the LED devices and the thickness of quantum barriers (QBs) was investigated. The crystal quality and surface cracking of GaN-on-Si were greatly improved by an AlxGa1-xN buffer layer composed of graded Al. The threading dislocation density of the GaN-on-Si LEDs was reduced to < 7 x 10(8) cm(-2), yielding LEDs with high internal quantum efficiency. Simulation results indicated that reducing the QB thickness improved the carrier injection rate and distribution, thereby improving the droop behavior of the LEDs. LEDs featuring 6-nm-thick QBs exhibited the lowest droop behavior. However, the experimental results showed an unanticipated phenomenon, namely that the peak external quantum efficiency (EQE) and light output power (LOP) gradually decreased with a decreasing QB thickness. In other words, the GaN-on-Si LEDs with 8-nm-thick QBs exhibited low droop behavior and yielded a good peak EQE and LOP, achieving a 22.9% efficiency droop and 54.6% EQE. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Embedded InN Dot-Like Structure within InGaN Layers Using Gradient-Indium Content in Nitride-Based Solar Cell
(2013)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Tan, Ming-Hsuan
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Yeh, Yun-Ling
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Lin, Da-Wei
The novel design of embedded InN dot-like structure within InGaN was useful as an absorption layer in photovoltaic (PV) cells. We constructed the simulation model by employing the commercial software APSYS (R) and integrating the absorption coefficient of thin InN materials fabricated by metal organic vapor deposition (MOCVD). The model of simulating gradient Indium content of InGaN used as transition interface between InN and GaN was investigated. The results exhibit utilizing the effective variation of Indium content and suitable thickness to approach the optimal characteristic of hybrid InN/InGaN structure within solar cells shall be anticipated to enhance the performance of current nitride-based solar cells.
Embedded InN Dot-Like Structures with Modulating Growth Temperature in Nitride-Based Solar Cell
(2014-01-01)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Kuo, Hao-Chung
The embedded InN dot-like structures within nitride-based solar cells is promising for extended visible and infrared absorption of solar spectrum. The temperature dependent InN epitaxial growth was demonstrated in a low-pressure metal organic chemical vapor deposition (MOCVD) system and the absorption coefficient of fabricated InN-dots was measured and integrated into APSYS (R) simulation platform. The dimension-quantization effect of the InN dot-like layer was investigated via photoluminescence (PL) measurements. Higher growth temperature region induces multiple PL peaks and blue-shift phenomenon, which could be attributed to variations in size and composition. The extracted absorption coefficients of InN-dot-like layer can be used to calculate the conversion efficiency of 2.34% for the corresponding GaN-based solar cell design.
Enhanced Light Output Power and Growth Mechanism of GaN-Based Light-Emitting Diodes Grown on Cone-Shaped SiO2 Patterned Template
(2013-04-01)
Lin, Da-Wei
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Huang, Jhih-Kai
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Lee, Chia-Yu
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Chang, Ruey-Wen
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Lan, Yu-Pin
In this study, we successfully transferred the patterns of a cone-shaped patterned sapphire substrate (CPSS) into SiO2 layer to fabricate a cone-shaped SiO2 patterned template by using nanoimprint lithography (NIL). The GaN-based light-emitting diodes (LEDs) were grown on this template by metal-organic chemical vapor deposition (MOCVD). The transmission electron microscopy (TEM) images suggest that the stacking faults formed near the cone-shaped SiO2 patterns during the epitaxial lateral overgrowth (ELOG) can effectively suppress the threading dislocations, which results in an enhancement of internal quantum efficiency. The Monte Carlo ray-tracing simulation reveals that the light extraction efficiency of the LED grown on cone-shaped SiO2 patterned template can be enhanced as compared with the LED grown on CPSS. As a result, the light output power of the LED grown on cone-shaped SiO2 patterned template outperformed the LED grown on CPSS.
Enhanced photocurrent of a nitride-based photodetector with InN dot-like structures
(2014-12-01)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Lo, Yen-Hua
The InN dot-like layer was applied in the gallium nitride based material for the purpose of infrared photodetectors (PDs). This InN layer was grown by a low-pressure metal organic chemical vapor deposition technology under different growth temperatures. The X-ray diffraction patterns provide the information of crystal structure and the hexagonal orientation was detected. The Raman shifts and photoluminescence were also used to characterize the quality of InN film. Finally, the fabricated Schottky-type photodetector was tested under a solar simulator and a long-wavelength laser (lambda = 1550nm). The measurements show a highly linear relation between photo-generated currents and laser powers for the wavelength of 1550 nm. In the photonic detection range suitable for optical fiber communiation, a quantum efficiency of 9.2% can be observed. (C) 2014 Optical Society of America
GaN-Based Resonant-Cavity LEDs Featuring a Si-Diffusion-Defined Current Blocking Layer
(2014-12-15)
Yeh, Pinghui Sophia
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Yu, Meng-Chun
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Lin, Jia-Huan
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Huang, Ching-Chin
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Liao, Yen-Chao
GaN-based resonant-cavity light-emitting diode (RCLED) featuring a Si-diffusion-defined confinement structure is reported for the first time. The charge-coupled device images exhibited round, bright spots of sizes corresponding to the diffusion-defined aperture sizes under continuous-wave high-current-density operation and at room temperature. The full widths at half maximum of the electroluminescence spectra were 2 and 1.5 nm for 10-and 5-mu m-diameter RCLEDs, respectively. A stable peak wavelength of 406.6 nm was maintained at various injection currents. The results suggest Si diffusion is an effective means to reduce aperture size. The design and fabrication of the devices are described.
Greatly Improved Carrier Injection in GaN-based VCSEL by Multiple Quantum Barrier Electron Blocking Layer
(2015)
Hsieh, Dan-Hua
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Tzou, An-Jye
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Lin, Da-Wei
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Kao, Tsung-Sheng
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Lin, Chien-Chung
In this report, the fabrication and characteristics of III-nitride based vertical-cavity surface-emitting laser (VCSEL) with bulk AlGaN and AlGaN/GaN superlattice electron blocking layer (EBL) are observed experimentally and theoretically. The results have been revealed that laser performance is improved by using superlattice EBL. The output power and the slope efficiency are enhanced by the improvement of carrier injection into active region. And the reduction of threshold current density from 10 to 8 kA/cm2 is also observed. Theoretical calculation results suggest that the improved carrier injection efficiency can be mainly attributed to the partial release of the strain at the interface of last quantum barrier and superlattice EBL and hence the increase of electrons and holes effective barrier height.
Greatly Improved Efficiency Droop for InGaN-Based Green Light Emitting Diodes by Quaternary Content Superlattice Electron Blocking Layer
(2015)
Lin, Da-Wei
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Tzou, An-Jye
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Huang, Jhih-Kai
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Lin, Bing-Cheng
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Chang, Chun-Yen
We presented a low efficiency droop behavior green light emitting diodes (LEDs) with a quaternary content InAlGaN/GaN superlattice electron blocking layer (SL-EBL). The light output power shows a 57% enhancement and only 30% efficiency droop, which is attributed to a smooth band bending with a uniform carrier distribution.
Growth of semi-polar GaN-based light-emitting diodes grown on an patterned Si substrate
(2011)
Chiu, Ching-Hsueh
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Lin, Da-Wei
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Li, Zhen-Yu
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Ling, Shih-Chun
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Kuo, Hao-Chung
We present a study of semi-polar (1 (1) over bar 01) InGaN-based light emitting diodes (LEDs) grown on patterned (001) Si substrates by atmospheric-pressure metal organic chemical vapor deposition. A transmission electron microscopy image of the semi-polar template shows that the threading dislocation density was decreased significantly. From electroluminescence measurement, semi-polar LEDs exhibit little blue-shift and low efficiency droop at a high injection current because the reduction of the polarization field not only made the band diagram smoother but also restricted electron overflow to the p-GaN layer as shown in simulations. These results indicate that semi-polar InGaN-based LEDs can possess a high radiative recombination rate and low efficiency droop at a high injection current.
High Efficiency GaN-based Light Emitting Diodes with Embedded Air Voids/SiO2 Nanomasks
(2012-01-01)
Chiu, Ching-Hsueh
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Chen, Yan-Hao
We fabricated high efficiency LEDs with embedded micro-scale air voids and SiO2 nanomask exhibit smaller reverse-bias current and great enhancement of the light output (65% at 20mA) compared with the conventional LEDs.
High Reflectance Patterned Substrate Designed for Optical Devices
(2015)
Lan, Yu-Pin
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Wu, Yung-Chi
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Lin, Da-Wei
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Hong, Kuo-Bin
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Lee, Chia-Yu
This article proposed an approach by using patterned sapphire substrate to act as a 2-dimensional distributed Bragg reflector (DBR) mirror to increase the output power of LEDs.
High-Efficiency and Crack-Free InGaN-Based LEDs on a 6-inch Si (111) Substrate With a Composite Buffer Layer Structure and Quaternary Superlattices Electron-Blocking Layers
(2014-05-01)
Li, Zhen-Yu
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Lee, Chia-Yu
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Lin, Da-Wei
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Lin, Bing-Cheng
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Shen, Kun-Ching
In this paper, a composite buffer layer structure (CBLS) with multiple AlGaN layers and grading of Al composition/u-GaN1/(AlN/GaN) superlattices/u-GaN2 and InAlGaN/AlGaN quaternary superlattices electron-blocking layers (QSLs-EBLs) are introduced into the epitaxial growth of InGaN-based light-emitting diodes (LEDs) on 6-inch Si (111) substrates to suppress cracking and improve the crystalline quality and emission efficiency. The effect of CBLS and QSLs-EBL on the crystalline quality and emission efficiency of InGaN-based LEDs on Si substrates was studied in detail. Optical microscopic images revealed the absence of cracks and Ga melt-back etching. The atomic force microscopy images exhibited that the root-meansquare value of the surface morphology was only 0.82 nm. The full widths at half maxima of the (0002) and (1012) reflections in the double crystal X-ray rocking curve were similar to 330 and 450 arcs, respectively. The total threading dislocation density, revealed by transmission electron microscopy, was <6 x 10(8) cm(-2). From the material characterizations, described above, blue and white LEDs emitters were fabricated using the epiwafers of InGaNbased LEDs on 6-inch Si substrates. The blue LEDs emitter that comprised blue LEDs chip and clear lenses had an emission power of 490 mW at 350 mA, a wall-plug efficiency of 45% at 350 mA, and an efficiency droop of 80%. The white LEDs emitter that comprised blue LEDs chip and yellow phosphor had an emission efficiency of similar to 110 lm/W at 350 mA and an efficiency droop of 78%. These results imply that the use of a CBLS and QSLs-EBL was found to be very simple and effective in fabricating high-efficiency InGaN-based LEDs on Si for solid-state lighting applications.
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Hong, Kuo-Bin
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Lin, Da-Wei
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Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.