Browsing by Author "Chang, Shih-Pang"

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Characterization of a-plane green light-emitting diodes using nanorod lateral overgrowth
(2010)
Ling, Shih-Chun
;
Chang, Shih-Pang
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
We have demonstrated nanorod lateral overgrowth to reduce dislocation density in a-plane GaN. Subsequently, we grow green a-plane light-emitting diodes using nanorod lateral overgrowth. Output power of 0.5 mW was measured at 20 mA. (C)2010 Optical Society of America
Coreshell InGaN/GaN MQW Nanorod Photovoltaic Device
(2015)
Li, Yun-Jing
;
Tsai, Yu Lin
;
Chang, Jet-Rung
;
Chang, Shih-Pang
;
Lin, Chien-Chung
We report the fabrication and study of coreshell InGaN/GaN multiple quantum well (MQW) nanorod photovoltaic device. The nanorods were fabricated from a GaN substrate by top-down etch, followed by InGaN/GaN MQW growth. The 3D geometry allows higher Indium incorporation and extends the solar absorption spectral range as compared with a planar reference sample. The proof-of-concept coreshell nanorod photovoltaic device has a fill factor of about 54.2%, the short current density of 1.16 mA/cm(2), the open circuit voltage of 0.68 V, and the power conversion efficiency of 0.38%, respectively.
Efficiency and Droop Improvement in InGaN/GaN Light-Emitting Diodes by Selective Carrier Distribution Manipulation
(2012-04-01)
Wang, Chao-Hsun
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Chang, Shih-Pang
;
Ku, Pu-Hsi
;
Lan, Yu-Pin
;
Lin, Chien-Chung
Efficiency and droop behavior in InGaN/GaN light-emitting diodes (LEDs) are both improved using selectively graded composition multiple quantum barriers (SGQBs). Simulation results show that SGQBs could moderately improve the hole transport in the active region. In the meantime, the spatial distribution overlap between electrons and holes in the active region could also be well considered. Therefore, the radiative recombination of the SGQB LED is more efficient than that of the conventional LED. The overall efficiency and droop behavior are simultaneously improved in the SGQB LED, at both low and high current densities. (C) 2012 The Japan Society of Applied Physics
Efficiency and droop improvement in InGaN/GaN light-emitting diodes by selectively carrier-distribution manipulation
(2012)
Lin, Da-Wei
;
Wang, Chao-Hsun
;
Chang, Shih-Pang
;
Ku, Pu-Hsih
;
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.
Electrically driven green, olivine, and amber color nanopyramid light emitting diodes
(2013-10-07)
Chang, Shih-Pang
;
Chang, Jet-Rung
;
Sou, Kuok-Pan
;
Liu, Mei-Chun
;
Cheng, Yuh-Jen
We report the fabrication and studies of electrically driven green, olivine, and amber color nanopyramid GaN light emitting diodes (LEDs). InGaN/GaN multiple quantum wells (MQWs) were grown on the nanopyramid semipolar facets. Compared with the commonly used (0001) c-plane MQWs, the semipolar facet has lower piezoelectric field, resulting in much faster radiative recombination efficiency. This is important for high In content MQWs. The measured internal quantum efficiencies for green, olivine, and amber color LED are 30%, 25%, and 21%, respectively. The radiative and non-radiative lifetime of the semipolar MQWs are also investigated. (C) 2013 Optical Society of America
Growth and Electroluminescent Property of Multi-Facet InGaN/GaN Multiple Quantum Well Light Emitting Device
(2015)
Li, Yun-Jing
;
Chang, Shih-Pang
;
Cheng, Yuh-Jen
;
Kuo, Hao-Chung
;
Chang, Chun-Yen
We report the study of InGaN/GaN multiple quantum wells (MQWs) grown on multi-facet microrods. The multi-facet MQWs have broad emission spectrum. Electrical injection was demonstrated with emission color ranged from red to blue.
Highly Efficient InGaN-Based Light Emitting Devices grown on Nanoscale Patterned Substrates by MOCVD
(2011)
Lin, Chien-Chung
;
Chiu, Ching-Hsueh
;
Huang, H. W.
;
Chang, Shih-Pang
;
Kuo, Hao-Chung
Highly efficient InGaN-base light emitting diodes are crucial for next generation solid state lighting. However, drawbacks in substrate materials such as lattice and thermal expansion coefficient mismatches hold back the lamination efficiency improvement. In the past, patterned sapphire sustrate (PSS) has been proven to be effect to enhance the LED's performance. In this work, we reviewed several promising nano-scale technologies which successfully increase the output of LED through better material quality and light extraction. First, we presented a study of high-performance blue emission GaN LEDs using GaN nanopillars (NPs). It exhibits smaller blue shift in electroluminescent peak wavelength and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs. Secondly, GaN based LEDs with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated structure grown on sapphire substrate. At an injection current of 20mA, the LED with NHPSS increased the light output power of LEDs by 1.33 times, and the wall-plug efficiency is 30% higher at 20mA indicating that it had larger light extraction efficiency (LEE). Finally, we fabricated the high performance electrical pumping GaN-based semipolar {10-11} nano-pyramid LEDs on c-plane sapphire substrate by selective area epitaxy (SAE). The emission wavelength only blue-shifted about 5nm as we increased the forward current from 40 to 200mA, and the quantum confine stark effect (QCSE) had been remarkably suppressed on semipolar surface at long emission wavelength region. These results manifest the promising role of novel nanotechnology in the future III-nitride light emitters.
Highly Efficient InGaN-Based Light Emitting Devices grown on Nanoscale Patterned Substrates by MOCVD
(2012)
Lin, Chien-Chung
;
Chiu, Ching-Hsueh
;
Huang, H. W.
;
Chang, Shih-Pang
;
Kuo, Hao-Chung
Highly efficient InGaN-base light emitting diodes are crucial for next generation solid state lighting. However, drawbacks in substrate materials such as lattice and thermal expansion coefficient mismatches hold back the lamination efficiency improvement. In the past, patterned sapphire sustrate (PSS) has been proven to be effect to enhance the LED\'s performance. In this work, we reviewed several promising nano-scale technologies which successfully increase the output of LED through better material quality and light extraction. First, we presented a study of high-performance blue emission GaN LEDs using GaN nanopillars (NPs). It exhibits smaller blue shift in electroluminescent peak wavelength and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs. Secondly, GaN based LEDs with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated structure grown on sapphire substrate. At an injection current of 20mA, the LED with NHPSS increased the light output power of LEDs by 1.33 times, and the wall-plug efficiency is 30% higher at 20mA indicating that it had larger light extraction efficiency (LEE). Finally, we fabricated the high performance electrical pumping GaN-based semipolar {10-11} nano-pyramid LEDs on c-plane sapphire substrate by selective area epitaxy (SAE). The emission wavelength only blue-shifted about Snm as we increased the forward current from 40 to 200mA, and the quantum confine stark effect (QCSE) had been remarkably suppressed on semipolar surface at long emission wavelength region. These results manifest the promising role of novel nanotechnology in the future III-nitride light emitters.
Improvement in efficiency droop of GaN-based light-emitting diodes by optimization of active regions
(2012)
Lin, Da-Wei
;
Wang, Chao-Hsun
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Chang, Shih-Pang
;
Chiu, Ching-Hsueh
;
Lan, Yu-Pin
In this paper, we propose several methods to improve the efficiency droop of GaN-based light-emitting diodes by optimization of active regions, such as alternative substrates, semi-polar MQWs, insertion layer, graded-thickness MQWs, and graded-composition EBL.
Influence of LT-GaN nucleation layer on the structural and optical properties of MOVPE-grown a-plane GaN
(2010-04-01)
Chang, Shih-Pang
;
Yang, Hung-Chih
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
The influence of the LT-GaN nucleation layer on the quality of the GaN template was investigated by the study of the surface morphology of the nucleation layer, and of the crystalline and optical properties of the subsequently grown a-plane GaN template. Both X-ray diffraction and photoluminescence results reveal that better crystalline and optical quality could be obtained using thinner nucleation layer thickness and higher V/III ratio, leading to brighter near band edge luminescence as compared to films grown on lower V/III ratio nucleation layer. Our experiments indicate that reduction in the density of nucleation layer islands can effectively improve the crystalline quality of a-plane GaN template, and the V/III ratio of nucleation layer is a more dominant growth parameter to improve the crystalline and optical quality at the same time. The optimized growth parameters for the nucleation layer in our study are thickness of 10 nm and V/III ratio of 9000. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
InGaN/GaN multiple-quantum-well nanopyramid-on-pillar light-emitting diodes
(2015-04-01)
Li, Yun-Jing
;
Chang, Jet-Rung
;
Chang, Shih-Pang
;
Sou, Kuok-Pan
;
Cheng, Yuh-Jen
We report the study of an electrically driven nanopyramid-on-pillar green light-emitting diode (LED). The pyramid-on-pillar nanostructure was fabricated by top-down etching from a GaN template, followed by epitaxial regrowth. High-In-content InGaN/GaN multiple quantum wells (MQWs) were grown on semipolar pyramid and nonpolar pillar surfaces. The measured radiative lifetimes of MQWs on these two surfaces were 2 orders of magnitude shorter than that of a conventional c-plane (0001) MQW owing to their lower polarization field. Electrical injection performance was also demonstrated and discussed. (C) 2015 The Japan Society of Applied Physics
Large-area ultraviolet GaN-based photonic quasicrystal laser with high-efficiency green color emission of semipolar {10-11} In0.3Ga0.7N/GaN multiple quantum wells
(2013-01-07)
Chen, Cheng-Chang
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Chiu, Ching-Hsueh
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Chang, Shih-Pang
;
Shih, M. H.
;
Kuo, Ming-Yen
In this study, a multi-color emission was observed from the large-area GaN-based photonic quasicrystal (PQC) nanopillar laser. The GaN PQC nanostructure was fabricated on an n-GaN layer by using nanoimprint lithographic technology. The regrown InGaN/GaN multiple quantum wells (MQWs) formed a nanopyramid structure on top of the PQC nanopillars. A lasing action was observed at ultraviolet wavelengths with a low threshold power density of 24 mJ/cm(2), and a green color emission from InGaN/GaN MQWs was also achieved simultaneously. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775373]
Lasing action in gallium nitride photonic quasicrystal nanorod arrays
(2012)
Chang, Shih-Pang
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Sou, Kuok-Pan
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Chang, Jet-Rung
;
Cheng, Yuh-Jen
;
Li, Yuh-Jing
We report the observation of lasing action from optically pumped gallium nitride nanorod arrays in a quasicrystal pattern. The nanorods were fabricated from a GaN substrate by nanoimprint patterned etching, followed by epitaxial regrowth to form crystalline facets. The imprint was a 12-fold symmetric quasicrystal pattern. The regrowth grew a multiple quantum well core-shell structure on nanorods. The cathodoluminescent emission of quantum wells red shifts from the bottom to top region of nanorod. Under optical pumping, multiple lasing peaks were observed. The lasing modes formed by 12-fold symmetric photonic quasicrystal nanorod arrays are discussed.
Lasing action in gallium nitride quasicrystal nanorod arrays
(2012-05-21)
Chang, Shih-Pang
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Sou, Kuok-Pan
;
Chen, Chieh-Han
;
Cheng, Yuh-Jen
;
Huang, Ji-Kai
We report the observation of lasing action from an optically pumped gallium nitride quasicrystal nanorod arrays. The nanorods were fabricated from a GaN substrate by patterned etching, followed by epitaxial regrowth. The nanorods were arranged in a 12-fold symmetric quasicrystal pattern. The regrowth grew hexagonal crystalline facets and core-shell multiple quantum wells (MQWs) on nanorods. Under optical pumping, multiple lasing peaks resembling random lasing were observed. The lasing was identified to be from the emission of MQWs on the nanorod sidewalls. The resonant spectrum and mode field of the 12-fold symmetric photonic quasicrystal nanorod arrays is discussed. (C) 2012 Optical Society of America
Light Output Enhancement of GaN-Based Light-Emitting Diodes by Optimizing SiO2 Nanorod-Array Depth Patterned Sapphire Substrate
(2012-04-01)
Chiu, Ching-Hsueh
;
Tu, Po-Min
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Chang, Shih-Pang
;
Lin, Chien-Chung
;
Jang, Chung-Ying
In this study, we investigated high-efficiency InGaN/GaN light-emitting diodes (LEDs) grown on sapphire substrates with SiO2 nanorod arrays (NRAs) of different heights. The GaN film showed an improved crystal quality through X-ray diffraction (XRD) full-width at half-maximum (FWHM), photoluminescence (PL), and cathodoluminescence (CL) measurements. The light output power and internal quantum efficiency (IQE) of the fabricated LEDs were increased when compared with those of conventional LEDs. Transmission electron microscopy (TEM) images suggested that the voids between SiO2 nanorods and the stacking faults introduced during the nanoscale epitaxial lateral overgrowth (NELOG) of GaN can effectively reduce the threading dislocation density (TDD). We believe that the improvements could be attributed to both the enhanced light extraction by utilizing SiO2 NRAs and the improved crystal quality through the NELOG method. We found that the sample with SiO2 NRA structures of 200 nm height can increase the LED output power by more than 70% in our study. (C) 2012 The Japan Society of Applied Physics
Low Droop Nonpolar GaN/InGaN Light Emitting Diode Grown on m-Plane GaN Substrate
(2010)
Chang, Shih-Pang
;
Lu, Tien-Chang
;
Zhuo, Li-Fu
;
Jang, Chung-Ying
;
Lin, Da-Wei
The low droop nonpolar m-plane InGaN/GaN light emitting diode (LED) has been fabricated and investigated. The external quantum efficiency for a 300x300 mu m square LED chip only drops about 18% from maximum at an operation current of 22 A/cm(2) (20 mA) to 330 A/cm(2) (300 mA) dc operations at room temperature. In addition, the internal quantum efficiency has been extracted by temperature-dependent photoluminescence measurements, and there is no droop observed as the carrier density increases. The small droop in efficiency of m-plane LEDs could be due to the lack of polarization effects that enhances the carrier confinement under high current density operation. The polarization anisotropy is clearly observed in the m-plane LED, and the degree of polarization is 68%.
Low Efficiency Droop Green Nano-Pyramid {10(1)over-bar1} InGaN/GaN Multiple Quantum Well LED
(2014)
Chang, Shih-Pang
;
Xiong, Kang-lin
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Lin, Da-Wei
;
Cheng, Yuh-Jen
;
Han, Jung
We report a low efficiency droop 520 nm green nano-pyramid InGaN/GaN multiple quantum well (MQW) LED. MQWs were grown on the semipolar {10 (1) over bar1} nano-pyramid facets. The device physics will be discussed in details.
Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes
(2010-06-07)
Ling, Shih-Chun
;
Lu, Tien-Chang
;
Chang, Shih-Pang
;
Chen, Jun-Rong
;
Kuo, Hao-Chung
We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm(2), the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3449557]
Low efficiency droop of InGaN/GaN blue LEDs with super-lattice active structure
(2012)
Chang, Shih-Pang
;
Sou, Kuok-Pan
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Chang, Jet-Rung
;
Cheng, Yuh-Jen
;
Li, Yuh-Jing
We report the efficiency droop behaviors of InGaN/GaN blue LEDs with different thickness of GaN quantum barriers (QBs). The droop percentage from efficiency peak to 70 A/cm(2) is only about 10% as reducing the thickness of GaN QBs from 104 angstrom to 33 angstrom. A less carrier localization has been observed from wavelength dependent time resoled photoluminescence measurement as reducing the thickness of GaN QBs. The alleviation of droop percentage may due to more uniform distribution of electron and hole carrier in the active region, which resulted from super-lattice (SL) like active structure. The crystalline quality does not become worse from the results of v-pits density even thickness of GaN QBs is as low as 33 angstrom. The SL like active structure could be a potential structure to alleviate the efficiency droop for the application of solid state general lighting.
Multifacet Microrod Light-Emitting Diode With Full Visible Spectrum Emission
(2016-09)
Li, Yun-Jing
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Chang, Jet-Rung
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Chang, Shih-Pang
;
Lin, Bo-Wen
;
Yeh, Yen-Hsien
We demonstrated a full visible spectrum emission from a 3D multifacet microrod light-emitting diode (LED). The microrods were fabricated by top-down patterned etched and regrowth. Hexagonal {11-20} and {11-22} facets were first formed on the microrods, then gradually transformed to {10-10} and {10-11} facets. This facet evolution was attributed to the growth competition among different crystal planes. The multiple quantum wells grown on the microrods also followed this facet evolution and resulted in broad emission spectrum. The device can have direct white light emission covering full visible spectral range from 460 to 660 nm under electrical injection.