共查询到20条相似文献,搜索用时 15 毫秒
1.
High light-extraction (external quantum efficiency ~40%) 465-nm GaN-based vertical light-emitting diodes (LEDs) employing double diffuse surfaces were fabricated. This novel LED structure includes one top transmitted diffuse surface and another diffuse omnidirectional reflector (ODR) on the bottom of a LED chip. The diffusive ODR consists of a roughened p-type GaN layer, an indium-tin-oxide (ITO) low refractive index layer, and an Al layer. The surface of the p-type GaN-layer was naturally roughened while decreasing the growth temperature to 800 degC. After flip-bonding onto a Si substrate by AuSn eutectic metal and laser lift-off processes to remove the sapphire substrate, an anisotropic etching by dilute potassium hydroxide (KOH) was employed on the N-face n-GaN layer to obtain transmitted diffuse surfaces with hexagonal-cone morphology. The double diffused surfaces LEDs show an enhancement of 56% and 236% in light output power compared to single side diffused surface and conventional LEDs, respectively. The devices also show a low leakage current in the order of magnitude of 10 -8 A at -5 V and a calculated external quantum efficiency of about 40%. The high scattering efficiency of double diffused surfaces could be responsible for the enhancement in the device light output power 相似文献
2.
《Lightwave Technology, Journal of》2009,27(12):1985-1989
3.
Ching-Hua Chiu Ming-Hua Lo Tien-Chang Lu Peichen Yu Huang H.W. Hao-Chung Kuo Shing-Chung Wang 《Lightwave Technology, Journal of》2008,26(11):1445-1454
We have developed a simple method to fabricate nanoscale masks by using self-assembly Ni clusters formed through a rapid thermal annealing (RTA) process. The density and dimensions of the Ni nano-masks could be precisely controlled. The nano-masks were successfully applied to GaN-based light-emitting diodes (LEDs) with nano-roughened surface, GaN nanorods, and GaN-based nanorod LEDs to enhance light output power or change structure properties. The GaN-based LED with nano-roughened surface by Ni nano-masks and excimer laser etching has increased 55% light output at 20 mA when compared to that without the nano-roughened process. The GaN nanorods fabricated by the Ni nano-masks and ICP-RIE dry etching showed 3.5 times over the as-grown sample in photoluminescence (PL) intensity. The GaN-based nanorod LEDs assisted by photo-enhanced chemical (PEC) wet oxidation process were also demonstrated. The electroluminescence (EL) intensity of the GaN-based nanorod LED with PEC was about 1.76 times that of the as-grown LED. The fabrication, structure properties, physical features, and the optical and electrical properties of the fabricated devices will be discussed. 相似文献
4.
Huang S.-H. Horng R.-H. Wen K.-S. Lin Y.-F. Yen K.-W. Wuu D.-S. 《Photonics Technology Letters, IEEE》2006,18(24):2623-2625
A novel flip-chip structure of GaN-sapphire light-emitting diodes (LEDs) was developed to improve the external quantum efficiency, where the sapphire substrate was textured and shaped with beveled sidewalls using a wet etching technique. The forward voltage of the conventional flip-chip and shaped flip-chip GaN LEDs were 2.84 and 2.85 V at 20 mA, respectively. This indicates that the GaN LED was not destroyed during the sapphire wet etching process. It was found that the output power increased from 9.3 to 14.2 mW, corresponding to about 52% increases in the external quantum efficiency. The results agree well with the simulation data that the shaped flip-chip GaN LED can provide better light extraction efficiency than that of the conventional flip-chip sample 相似文献
5.
《Electron Device Letters, IEEE》2009,30(5):496-498
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7.
Chia-Ming Lee Chang-Cheng Chuo I-Ling Chen Jui-Cheng Chang Jen-Inn Chyi 《Electron Device Letters, IEEE》2003,24(3):156-158
Unlike the conventional layer structure of an InGaN-GaN multiple-quantum-well light-emitting diode (LED), an LED with reversed p-type and n-type layer sequence, and an n+/p+ tunnel junction has been investigated. When operated at 20 mA, the output power of the inverted LED is almost twice that of the conventional LED. Since the structures of these two LEDs are alike when analyzed by X-ray diffraction, the improvement in the light intensity could be attributed to the elimination of the absorption/reflection by the transparent conductive layer and/or some quality improvement of p-type GaN in the inverted LED. 相似文献
8.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
9.
Zengcheng Li Bo Feng Biao Deng Legong Liu Yingnan Huang Meixin Feng Yu Zhou Hanmin Zhao Qian Sun Huaibing Wang Xiaoli Yang Hui Yang 《半导体学报》2018,(4):39-43
This work reports the fabrication of via-thin-film light-emitting diode (via-TF-LED) to improve the light output power (LOP) of blue/white GaN-based LEDs grown on Si (111) substrates.The as-fabricated via-TF-LEDs were featured with a roughened n-GaN surface and the p-GaN surface bonded to a wafer carrier with a silver-based reflective electrode,together with an array of embedded n-type via pillar metal contact from the p-GaN surface etched through the multiple-quantum-wells (MQWs) into the n-GaN layer.When operated at 350 mA,the via-TF-LED gave an enhanced blue LOP by 7.8% and over 3.5 times as compared to the vertical thin-film LED (TF-LED) and the conventional lateral structure LED (LS-LED).After covering with yellow phosphor that converts some blue photons into yellow light,the via-TF-LED emitted an enhanced white luminous flux by 13.5% and over 5 times,as compared with the white TF-LED and the white LS-LED,respectively.The significant LOP improvement of the via-TF-LED was attributed to the elimination of light absorption by the Si (111) epitaxial substrate and the finger-like n-electrodes on the roughened emitting surface. 相似文献
10.
Lee Y.J. Kuo H.C. Wang S.C. Hsu T.C. Hsieh M.H. Jou M.J. Lee B.J. 《Photonics Technology Letters, IEEE》2005,17(11):2289-2291
An n-side-up AlGaInP-based light-emitting diode (LED) with a triangle-like surface morphology was fabricated using the adhesive layer bonding technique, followed by wet etching to roughen the surface. The light output power of the roughened-surface LED was 1.6 times higher than that of a flat-surface LED at an injection current of 20 mA, i.e., a significant improvement attributed to the ability of the roughened surface to not only reduce the internal reflection between the rear mirror system and the semiconductor-air interface, but also to effectively scatter the light outside the LED device. 相似文献
11.
Yan Shen Huayong Xu Xiangang Xu Qing Liu Huan Liu Kai Jiang Xiaobo Hu 《Materials Science in Semiconductor Processing》2013,16(6):1719-1722
A thin film consisting of a disordered nanorod network of indium tin oxide (ITO) and conventional ITO films are fabricated on gallium nitride (GaN) based-light emitting diodes (LEDs) by electron beam evaporation. The surface morphologies are observed by scanning electron microscopy (SEM). The disordered nanorod network of ITO is grown in vacuum without oxygen. It can be applied directly on the LED as the current spreading film unlike other nanorods which require growth on a conductive layer. The transmittance, current–voltage characteristic, and the dependence of light output power on current are measured for disordered nanorod network ITO LEDs and conventional ITO LEDs, respectively. The measurement results indicate that the nanorod network provides a significant improvement in the light output power of GaN-based LEDs. The influence of the structure of ITO films on the light output power of GaN-based LEDs is discussed. 相似文献
12.
Nano-hole patterned sapphire substrates (NHPSSs) were successfully prepared using a low-cost and high-efficiency approach, which is the laser interference lithography (LIL) combined with reactive ion etching (RIE) and inductively coupled plasma (ICP) techniques. Gallium nitride (GaN)-based light emitting diode (LED) structure was grown on NHPSS by metal organic chemical vapor deposition (MOCVD). Photoluminescence (PL) measurement was conducted to compare the luminescence efficiency of the GaN-based LED structure grown on NHPSS (NHPSS-LED) and that on unpatterned sapphire substrates (UPSS-LED). Electroluminescence (EL) measurement shows that the output power of NHPSS-LED is 2.3 times as high as that of UPSS-LED with an injection current of 150 mA. Both PL and EL results imply that NHPSS has an advantage in improving the crystalline quality of GaN epilayer and light extraction efficiency of LEDs at the same time. 相似文献
13.
《Quantum Electronics, IEEE Journal of》2008,44(11):1116-1123
14.
Chung-Chieh Yang Chia-Feng Lin Jen-Hao Chiang Hsun-Chih Liu Chun-Min Lin Feng-Hsu Fan Chung-Ying Chang 《Journal of Electronic Materials》2009,38(1):145-152
InGaN-based light-emitting diodes (LEDs) were fabricated to have a higher light extraction through the photoelectrochemical
(PEC) mesa shaping process. After the PEC selective wet oxidation and wet etching processes, stable and controllable crystallographic
etching planes were formed as p-type GaN {} planes and n-type GaN {} planes included at an angle of 27 deg. The ever-present cone-shaped structure of a PEC-treated LED has a larger light scattering
area and higher light extraction cones on the mesa sidewall, as analyzed by microphotoluminescence and light output power
measurement. This cone-shaped-sidewall LED has a higher light output power and a larger divergence angle compared with a conventional
LED measured in an LED chip form. 相似文献
15.
Wei-Chih Lai Chen P.H. Chang L.C. Cheng-Huang Kuo Jinn-Kong Sheu Tun C.J. Shei S.C. 《Photonics Technology Letters, IEEE》2009,21(18):1293-1295
In this letter, the authors report the fabrication of GaN-based light-emitting diodes (LEDs) with mesh indium-tin-oxide p-contact and nanopillars on patterned sapphire substrate. Using hydrothermal ZnO nanorods as the etching hard mask, the authors successfully formed vertical GaN nanopillars inside the mesh regions and on the mesa-etched regions. It was found that 20-mA forward voltage and reverse leakage currents observed from the proposed LED were only slightly larger than those observed from the conventional LEDs. It was also found that output power of the proposed LED was more than 80% larger than that observed from conventional LED prepared on flat sapphire substrate. 相似文献
16.
Ming-Kwei Lee Chen-Lin Ho Po-Chun Chen 《Photonics Technology Letters, IEEE》2008,20(4):252-254
We investigate the light extraction efficiency of a GaN light-emitting diode (LED) by using liquid-phase-deposited ZnO rods at near-room temperature. Zinc nitrate and hexamethylenetetramine were used as the deposition precursors. Compared with the conventional GaN LED, the optical power output of the GaN LED with crystalline ZnO rods on its surface has about 1.6 times enhancement. 相似文献
17.
In this letter, lateral GaN-based Light Emitting Diodes (LEDs) with a SiO2 current blocking layer (CBL) buried in the indium tin oxide (ITO) film and highly reflective metal materials have been proposed. Compared with the conventional CBL structure which was inserted between ITO film and p-type GaN, simulation results showed that LEDs with a buried CBL in the ITO film effectively facilitated current spreading under the CBL. We demonstrated that buried CBL was beneficial for suppressing current crowding (CC) effect around the edge of CBL and may facilitate higher LED efficiency. Furthermore, experimental results showed that LEDs with the buried structure we proposed showed lower working voltage and higher light output power (LOP) compared with those with conventional CBL structure. These results further confirmed that the buried CBL scheme was effective to reduce current crowding (CC) effect. In addition, highly reflective metal materials of Cr/Al/Pt/Au were employed to reduce light absorption and achieve high light extraction efficiency. 相似文献
18.
In this letter, a GaN/sapphire light-emitting diode (LED) structure was designed with improved electrostatic discharge (ESD) performance through the use of a shunt GaN ESD diode connected in inverse-parallel to the GaN LED. Thus, electrostatic charge can be discharged from the GaN LED through the shunt diode. We found that the ESD withstanding capability of GaN/sapphire LEDs incorporating this ESD-protection feature could be increased from several hundreds up to 3500 V in the human body model. Furthermore, flip-chip (FC) technology was also used to produce ESD-protected LEDs to further improve light output power and reliability. At a 20-mA current injection, the output power of the FC LEDs showed an improvement of around 60%. After a 1200-h aging test, the luminous intensities of the FC LEDs featuring an internal ESD-protection diode decreased by 4%. This decay percentage was far less than those of non-FC LEDs 相似文献
19.
Tsai C.M. Sheu J.K. Lai W.C. Hsu Y.P. Wang P.T. Kuo C.T. Kuo C.W. Chang S.J. Su Y.K. 《Electron Device Letters, IEEE》2005,26(7):464-466
GaN-based light-emitting diodes (LEDs) with naturally textured surfaces grown by MOCVD were demonstrated. In this study, a growth-interruption step and a surface treatment using biscyclopentadienyl magnesium (CP/sub 2/Mg) were simultaneously performed to form a plurality of nuclei sites on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface having truncated pyramids. Experimental results indicated that GaN-based LED with the truncated pyramids on the surface exhibited an enhancement in output power of 66% at 20 mA. It is worth noting that the typical 20-mA-driven forward voltage is only slightly higher than those of conventional LEDs (without the Mg-treatment process). 相似文献