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Significant Improvement of GaN Crystal Quality with Ex-situ Sputtered AlN Nucleation Layers
(2016-01-01)
Chen, Shuo-Wei
;
Yang, Young
;
Wen, Wei-Chih
;
Li, Heng
;
Lu, Tien-Chang
Ex-situ sputtered AlN nucleation layer has been demonstrated effective to significantly improve crystal quality and electrical properties of GaN epitaxy layers for GaN based Light-emitting diodes (LEDs). In this report, we have successfully reduced X-ray (102) FWHM from 240 to 110 arcsec, and (002) FWHM from 230 to 101 arcsec. In addition, reverse-bias voltage (Vr) increased around 20% with the sputtered AlN nucleation layer. Furthermore, output power of LEDs grown on sputtered AlN nucleation layer can be improved around 4.0% compared with LEDs which is with conventional GaN nucleation layer on pattern sapphire substrate (PSS).
Visible Light Positioning and Lighting Based on Identity Positioning and RF Carrier Allocation Technique Using a Solar Cell Receiver
(2016-08-01)
Hsu, Chin-Wei
;
Wu, Jhao-Ting
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Wang, Hao-Yu
;
Chow, Chi-Wai
;
Lee, Chun-Hsing
We propose and experimentally demonstrate an indoor positioning system which combines identity positioning and the radio frequency carrier allocation technique in order to reduce the signal interference from nearby light-emitting diodes (LEDs) and improve the accuracy of positioning. In addition, the solar cell is used as an optical receiver for the visible light positioning system. Due to the benefits of solar cells such as low-cost, high light sensitivity, and ease in integration with wearable devices, the proposed system could be an energy-efficient and environmentally friendly choice for indoor positioning in the future.
Structural Effects on Highly Directional Far-Field Emission Patterns of GaN-Based Micro-Cavity Light-Emitting Diodes With Photonic Crystals
(2010-10-01)
Lai, Chun-Feng
;
Kuo, Hao-Chung
;
Chao, Chia-Hsin
;
Yu, Peichen
;
Yeh, Wen-Yung
This study theoretically and experimentally investigates the highly directional far-field emission patterns of GaN photonic crystal (PhC) micro-cavity light-emitting diodes (MCLEDs) depending on varying structural parameters. Angular-spectra-resolved electroluminescence measurements reveals the behavior of guided-mode extraction which is significantly affected by the structural parameters of GaN PhC MCLEDs, where the GaN cavity thickness decides the extracted guided mode numbers, PhC lattice constant influences the distribution of far-field emission, and PhC hole depth affects the interaction with guided modes. The proposed GaN ultrathin MCLED (uMCLED) with PhC lattice constant of 420 nm and deep hole depth of 250 nm exhibited a maximum output light extraction efficiency of 248% under one-watt input power compared to GaN non-PhC uMCLED and produced a directional far-field emission pattern at half intensity near +/- 17 degrees. The present results indicate that highly directional light extraction enhancement could contribute to developments of many applications, especially for etendue-limited applications such as pico-projectors.
Highly reliable GaN-based light-emitting diodes formed by p-In0.1Ga0.9N-ITO structure
(2004-08-01)
Chang, KM
;
Chu, JY
;
Cheng, CC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Indium-tin-oxide (ITO) is deposited as a transparent current spreading layer of GaN-based light-emitting diodes (LEDs). To reduce the interfacial Schottky barrier height, a thin p-In0.1Ga0.9N layer is grown as an intermediate between ITO And p-GaN. The contact resistivity around 2.6 x 10(-2) Omega . cm(2) results in a moderately high forward voltage LED of 3.43 V operated at 20 mA. However, the external quantum efficiency and power efficiency are enhanced by 46% and 36%, respectively, in comparison with the conventional Ni-Au contact LEDs. In the life test, the power degradation of the p-In0.1Ga0.9N-ITO contact samples also exhibits a lower value than that of the conventional ones.
Planar Lighting System Using Array of Blue LEDs to Excite Yellow Remote Phosphor Film
(2011-01-01)
Huang, Hsin-Tao
;
Huang, Yi-Pai
;
Tsai, Chuang-Chuang
;
光電工程學系
;
顯示科技研究所
This investigation demonstrates a novel light-emitting system with an array of blue light-emitting diodes (LEDs). Unlike a conventional lighting system that is constructed from white LEDs, the proposed planar lighting system uses blue LEDs to excite a YAG : Ce(3+) yellow phosphor film remotely, yielding a high lumen efficiency with uniform and planar light-emission. The phosphor film herein acts as a wavelength converter and a light diffuser simultaneously. The optical properties of the proposed lighting system, angular color deviation and light-emitting uniformity, are studied. Eventually, a high lumen efficiency (73.0 lm/W) and thin lighting module (7.5 mm-thick) was demonstrated without the use of any conventional diffuser plate or light guiding plate (LGP). A low color deviation (Delta u'v' = 0.025) and a high light-emitting uniformity (U(niformity) = 82%) were achieved. Hence, the proposed lighting system exhibited superior optical performance using a compact module.
Spatial Correlation Between Efficiency and Crystal Structure in GaN-Based Light-Emitting Diodes Prepared on High-Aspect Ratio Patterned Sapphire Substrate With Sputtered AlN Nucleation Layer
(2014-07-01)
Chang, Li-Chuan
;
Chen, Yu-An
;
Kuo, Cheng-Huang
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
In this paper, we investigate sputtered physical vapor deposition (PVD) AlN nucleation layer effects on crystal quality and efficiency of GaN-based light-emitting diodes (LEDs) prepared on high-aspect ratio patterned sapphire substrate (HARPSS). The crystal quality of the GaN epitaxial layer prepared on HARPSS with a PVD AlN nucleation layer was significantly better than that with a conventional metal organic chemical vapor deposition (MOCVD)-grown AlN nucleation layer. In addition, the pure wurzite structure GaN prepared on HARPSS could be obtained using PVD AlN nucleation layer. With the PVD AlN nucleation layer, the 20-mA LED light output power of the LEDs can be enhanced by 47.7% compared with the LEDs with the conventional MOCVD-grown AlN nucleation layer.
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
;
Lee, Chia-Yu
;
Lin, Da-Wei
;
Lin, Bing-Cheng
;
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.
Investigation and Comparison of the GaN-Based Light-Emitting Diodes Grown on High Aspect Ratio Nano-Cone and General Micro-Cone Patterned Sapphire Substrate
(2013-12-01)
Huang, Jhih-Kai
;
Lin, Da-Wei
;
Shih, Min-Hsiung
;
Lee, Kang-Yuan
;
Chen, Jyun-Rong
In this paper, we demonstrated the high performance GaN-based LEDs by using a high aspect ratio cone-shape nano-patterned sapphire substrate (HAR-NPSS). We utilized nano-imprint lithography (NIL) and dry-etching system to fabricate a high depth HAR-NPSS. The micro-scale patterned sapphire substrate (PSS) was also used for comparison. A great enhancement of light output was observed when GaN-based LEDs were grown on a HAR-NPSS or a PSS. The light output power of LEDs with a HAR-NPSS and LEDs with a PSS were enhanced of 49 and 38% compared to LEDs with a unpatterned sapphire substrate. The high output power of the LED with a HAR-NPSS indicated that the technology of NAR-NPSS not only can improve the crystalline quality of GaN-based LEDs but also a promising development to a NPSS.
An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure
(2013-11-01)
Chen, Kuo-Ju
;
Chen, Hsin-Chu
;
Lin, Chien-Chung
;
Wang, Chao-Hsun
;
Yeh, Chia-Chi
An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a (c) nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.
Design of a Hybrid Light Guiding Plate With High Luminance for Backlight System Application
(2013-12-01)
Pan, Jui-Wen
;
Hu, Ya-Wen
;
光電系統研究所
;
生醫電子轉譯研究中心
;
Institute of Photonic System
We proposed a novel backlight system, which consisted of a hybrid light guide plate (LGP) and one diffuser sheet. The hybrid LGP contains a flat plate without any microstructures and one layer of optically patterned film (OPF). Comparing with the conventional edge-lit backlight system, the on-axis luminance could be improved to 6.1 x by using the novel backlight system and the half-luminance angle decreased from 21 deg to 10 deg in vertical direction, and decreased from 21 deg to 6 deg in horizontal direction. At the same time, this design also achieved a uniformity of illumination of 89%. The design can predigest the fabrication and reduce the number of components. Moreover, since the microstructures arrangement was periodical, user could use light-emitting diodes (LEDs) on the both sides. When user turned on both side LEDs, the on-axis luminance were improved 1.7 x comparing with turning on single side LEDs.

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