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Improved performance of 375 nm InGaN/AlGaN light-emitting diodes by incorporating a heavily Si-doped transition layer
(2012-01-01)
Huang, Shih-Cheng
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Shen, Kun-Ching
;
Tu, Po-Min
;
Wuu, Dong-Sing
;
Kuo, Hao-Chung
High performance 375-nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) was developed using a heavy Si-doping technique with metalorganic chemical vapor deposition (MOCVD). From the transmission electron microcopy (TEM) image, the dislocation density was reduced after inserting a heavily Si-doping growth mode transition layer (GMTL) between un-doped GaN layer and Si-doped Al0.02Ga0.98N contact layer. The internal quantum efficiency (IQE) of the sample with GMTL measured by power-dependent photoluminescence shows 39.4% improved compared with the sample without GMTL. When the vertical type LED chips (size: 1mmx1mm) driving by a 350-mA current, the output powers of the LEDs with and without GMTL were measured to be 286.7 mW and 204.2 mW, respectively. As much as 40.4% increased light output power was achieved. Therefore, using the GMTL to reduce dislocation defects would be a promising prospective for InGaN/AlGaN UV LEDs to achieve high internal quantum efficiency.
Large area lighting applications with organic dye embedded flexible film
(2015-01-01)
Lin, Huang-Yu
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Tu, Zong-Yi
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Ku, Pei-Cheng
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Lin, Chien-Chung
;
Kuo, Hao-Chung
A flexible large area lighting devices have been demonstrated by PDMS films. The (polydimethylsiloxane) PDMS films doped with organic/inorganic materials. The PDMS film is favorable due to its heat stability, good transparency, and flexibility. This study aimed to combine both organic and inorganic materials for flexible large area lighting applications. The architecture consists of blue LEDs coupled to a leaky waveguide that is covered with the PDMS film. The white light was generated with the poly (9, 9-dioctylfluorene-co-benzothiadiazole) F8BT blended into the PDMS slurry. Organic wavelength conversion materials were chosen owing to their ability to decompose in nature. The more conventional inorganic phosphors such as YAG are difficult to decompose and may present environmental issues which can bring concerns in many lighting applications. These flexible PDMS films had thicknesses of 100 mu m, 440 mu m, and 980 mu m. The resulting white light devices had color temperatures of 8944K, 4863K, and 4429K, respectively. In this study, we have also compared the performance of the organic versus conventional YAG phosphor embedded films.
Numerical analysis on the effect of electron blocking layer in 365-nm ultraviolet light-emitting diodes
(2015-01-01)
Chen, Fang-Ming
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Chang, Jih-Yuan
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Kuo, Yen-Kuang
;
Lin, Bing-Cheng
;
Kuo, Hao-Chung
For 365-nm ultraviolet light-emitting diodes (UV LEDs), an electron blocking layer (EBL) is usually utilized to mitigate electron overflow. However, using EBL might obstruct holes from injecting into the active region. Moreover, the large polarization field in conventional EBL might also pull down the effective barrier height for electrons, and thus the electrons could easily overflow to the p-side region. To solve the above drawbacks, in this study, the Al content and p-doping concentration of the EBL in typical 365-nm UV LEDs are investigated systematically. Specifically, designs of AlGaN/GaN superlattice EBL and Al-content-graded EBL are explored in detail.
Light emission characteristics of nonpolar a-plane GaN-based photonic crystal defect cavities
(2015-01-01)
Kao, Tsung Sheng
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Wu, Tzeng-Tsong
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Tsao, Che-Wei
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Lin, Jyun-Hao
;
Lin, Da-Wei
In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been demonstrated. By using a micro-photoluminescence (mu-PL) system operated at 77 K, the dominant resonant modes of the GaN-based PC defect cavities show high quality factor (Q) values in the light emission performance which can be up to 4.3x10(3). Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect cavities was measured to achieve around 64 % along the m crystalline direction.
Optical and electrical properties of GaN-based light emitting diodes grown on micro and nano-scale patterned Si substrate
(2011-01-01)
Chiu, Ching-Hsueh
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Lin, Chien-Chung
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Deng, Dongmei
;
Kuo, Hao-Chung
;
Lau, Kei-May
We investigate the optical and electrical characteristics of the GaN-based light emitting diodes (LEDs) grown on Micro and Nano-scale Patterned silicon substrate (MPLEDs and NPLEDs). The transmission electron microscopy (TEM) images reveal the suppression of threading dislocation density in InGaN/GaN structure on nano-pattern substrate due to nanoscale epitaxial lateral overgrowth (NELOG). The plan-view and cross-section cathodoluminescence (CL) mappings show less defective and more homogeneous active quantum well region growth on nano-porous substrates. From temperature dependent photoluminescence (PL) and low temperature time-resolved photoluminescence (TRPL) measurement, NPLEDs has better carrier confinement and higher radiative recombination rate than MPLEDs. In terms of device performance, NPLEDs exhibits smaller electroluminescence (EL) peak wavelength blue shift, lower reverse leakage current and decreases efficiency droop compared with the MPLEDs. These results suggest the feasibility of using NPSi for the growth of high quality and power LEDs on Si substrates.
Blue resonant-cavity light-emitting diode with half milliwatt output power
(2016-01-01)
Yeh, Pinghui S.
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Chang, Chi-Chieh
;
Chen, Yu-Ting
;
Lin, Da-Wei
;
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.
Self-assembled Ni nanodot on SiO2 film-a novel reactive ion etching mask for Si nanopillar formation on Si substrate
(2006-01-01)
Lin, Huang-Shen
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Kao, Chih-Chiang
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Kuo, Hao-Chung
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Wang, Shing-Chung
;
Lin, Gong-Ru
By rapid thermal annealing the Ni film evaporated on thin SiO2 layer covered Si substrate, we have successfully demonstrated the self-aggregation of two-dimensional randomized Ni nano-dots on Si wafer. The thin oxide layer prevents the formation of NiSi2 compounds and facilitates the self-assembly of Ni nanodots from retaining the thermal power on SiO2 layer. This greatly shrinks the annealing time required for metallic nanodot formation from > 10 min to < 30 sec. With the advantage of the self-assemble Ni/SiO2 nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of < 50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICPRIE) procedure. After removing Ni dots and the SiO2 film on the Si substrate, both the visible and near infrared photoluminescence from the Si nano-pillar sample were observed and analyzed.
Undoped InP sandwiched InGaAs p-i-n photodetector with partially p-doped photoabsorption layer grown on linearly graded metamorphic InxGa1-xP buffered GaAs substrate
(2006-01-01)
Liao, Yu-Sheng
;
Lin, Gong-Ru
;
Kuo, Hao-Chung
;
Feng, Milton
;
光電工程學系
A novel top-illuminated In0.53Ga0.47As p-i-n photodiodes, with the partially p-doped photoabsorption layer, grown on GaAs substrate by using a linearly graded metamorphic InxGa1-xP (x graded from 0.49 to 1) buffer layer is reported. The dark current, optical responsivities, noise equivalent power, and operational bandwidth of the MM-PINPD with aperture diameter of 60 mu m are 13 pA, 0.6 A/W, 3.4.10(-15) W/Hz(1/2), and 8 GHz, respectively, at 1550 nm. Under the illumination of 1.2-ps pulse-train, the measured impulse response is 41 ps and the frequency bandwidth is up to 8 GHz with heterodyne beating measurement. The low cost InGaAs photodiode with high current bandwidth product (350 mA center dot GHz, at 10 GHz) and bandwidth-efficient product (4.8 GHz center dot A/W) have been achieved.
Low threshold current, low resistance 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE
(2007-01-01)
Yu, Hsin-Chieh
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Wang, Jyh-Shyang
;
Su, Yan-Kuin
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Chang, Shoou-Jinn
;
Kuo, Hao-Chung
The processing technology of 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE will be demonstrated. The threshold currents of the fabricated devices with 10 mu m oxide-confined aperture are 0.7mA, which correspond to 890A/cm(2) threshold current density. And the threshold voltage of the device is 1.03V and maximum output power is 33 M. The series resistance is 85 Omega which is 10 times lower then our preliminary work and 3 times lower then intracavity contacted InAs-InGaAs quantum-dot VCSEL. This relatively lower resistance can even comparable with the best result reported in InGaAs oxide-confined VCSELs with intracavity contact.
Resonant-enhanced full-color emission of quantum-dot-based micro LED display technology
(2015-12-14)
Han, Hau-Vei
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Lin, Huang-Yu
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Lin, Chien-Chung
;
Chong, Wing-Cheung
;
Li, Jie-Ru
Colloidal quantum dots which can emit red, green, and blue colors are incorporated with a micro-LED array to demonstrate a feasible choice for future display technology. The pitch of the micro-LED array is 40 mu m, which is sufficient for high-resolution screen applications. The method that was used to spray the quantum dots in such tight space is called Aerosol Jet technology which uses atomizer and gas flow control to obtain uniform and controlled narrow spots. The ultra-violet LEDs are used in the array to excite the red, green and blue quantum dots on the top surface. To increase the utilization of the UV photons, a layer of distributed Bragg reflector was laid down on the device to reflect most of the leaked UV photons back to the quantum dot layers. With this mechanism, the enhanced luminous flux is 194% (blue), 173% (green) and 183% (red) more than that of the samples without the reflector. The luminous efficacy of radiation (LER) was measured under various currents and a value of 165 lm/Watt was recorded. (C)2015 Optical Society of America

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