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Now showing 1 - 10 of 96

Abnormal PL spectrum in InGaN MQW surface emitting cavity
(2008-01-01)
Chu, J. T.
;
Cheng, Y. -J.
;
Kuo, H. C.
;
Lu, T. C.
;
Wang, S. C.
We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final 200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 run In0.1Ga0.9N well. The peak emission of the as-grown MQWs sample was similar to 420nm. A dielectric distributed Bragg reflectors (DBR) were then coated on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk GaN bottom surface. The cavity has a quality factor of similar to 520 from 400-490nm. The device was pumped by a focused CW HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum centered at the designed MOW wavelength was observed as expected. However, when the focused position was moved toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the designed MQW wavelength.
Analysis of Strain Relaxation and Emission Spectrum of A Free-Standing GaN-based Nanopillar
(2008-01-01)
Wu, Yuh-Renn
;
Yu, Peichen
;
Chiu, C. H.
;
Chang, Cheng-Yu
;
Kuo, H. C.
We have made a, GaN-based single nanopillar with a, diameter of 300nm using the focused ion beam (FB) technique. The micro-photoluminescence (mu-PL) from the embedded GaN/InGaN multi-quantum wells reveals a blue shift of 68.3 meV in energy. In order to explain the spectrum shift, we have developed a valence force field model to study the strain relaxation mechanism in a, single GaN-based nanopillar structure. The strain distribution and strain induced polarization effect inside the multiple quantum wells is added to our self-consistent Poisson, drift-diffusion, and Schrodinger solver to study the spectrum shift of mu-PL.
Directional Light Extraction from Photonic Crystal Thin-film GaN Light-Emitting Diodes
(2009-01-01)
Chao, Chia-Hsin
;
Lai, Chun-Feng
;
Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
The light enhancement of PhC LEDs within the collection cone angle was obtained according to measured far-field patterns In a +/- 20 degrees collection cone, the collimated PhC LED was enhanced up to similar to 2.4.
GaN growth on Si(111) using simultaneous AlN/alpha-Si3N4 buffer structure
(2008-07-01)
Chang, Jet Rung
;
Yang, Tsung Hsi
;
Ku, Jui Tai
;
Shen, Shih Guo
;
Chen, Yi Cheng
In this study, we examined the growth of a simultaneous AIN/alpha-Si3N4 buffer layer for crack-free GaN growth oil a Si(111) substrate. The compressive stress in the AlN/alpha-Si3N4/Si(111) structure retards the cracking ill the GaN layer. It is demonstrated that the Al-preseeded layer is a critical factor for accornplishing AlN and the crystalline alpha-Si3N4 layer simultaneously. The effect of Al layer deposition time on the c-axis lattice constants of the subsequent AlN layer, and the effect of the crystalline alpha-Si3N4 layer oil GaN quality were investigated by X-ray diffraction analysis. The 1 : 2 lattice coincidently matches at the alpha-Si3N4(0001)/Si(111) interface, and the 5 : 2 coincident lattice interface at AlN(0001)/alpha-Si3N4(0001) reduces the lattice mismatch in the AIN/alpha Si3N4/Si(111) structure. The 5 : 4 coincident lattice in the AIN/alpha-Si3N4/Si(111) structure is related to the reduction in the tensile stress in the AIN epilayers. The thickness of crack-free GaN is 2.00 mu m. The full widths at half-maximum (FWHM) of the X-ray rocking curve and neutral-donor-bound exciton (D degrees X) are 1012arcsec and 5.90meV, respectively.
Efficiency enhancement of UV/blue light emitting diodes via nanoscaled epitaxial lateral overgrowth of GaN on a SiO2 nanorod-array patterned sapphire substrate
(2008-11-15)
Chiu, C. H.
;
Li, Zhen-Yu
;
Chao, C. L.
;
Lo, M. H.
;
Kuo, H. C.
High-quality GaN layer was successfully grown on a SiO2 nanorod-array patterned sapphire substrate (NAPSS) using metal-organic chemical vapor deposition by a nanoscaled epitaxial lateral overgrowth (NELO) method. From tunneling electron microscope images, well coalescence and turned dislocations are parallel to the surface direction were clearly observed. The Raman shift measurement shows the residual stress in GaN was greatly reduced from 1.359 to 0.652 GPa when compared to a GaN on flat sapphire substrate. Also, a high-efficiency GaN-based light-emitting diodes (LEDs) were demonstrated on the NELO NAPSS GaN, the respective output power and external quantum efficiency of the NELO NAPSS LEDs were estimated to be 22 mW and 40.2% at an injection current of 20 mA, showing an enhancement factor of 52% over conventional LEDs. The significant improvement resulted from both the enhanced light extraction assisted by the NAPSS, and the reduced dislocation densities using the NELO method. (c) 2008 Published by Elsevier B.V.
Fabrication and characterization of In0.25Ga0.75N/GaN multiple quantum wells embedded in nanorods
(2005-10-01)
Hsueh, TH
;
Sheu, JK
;
Huang, HW
;
Chang, YH
;
Ou-Yang, MC
ln(0.25)Ga(0.75)N/GaN multiple quantum wells embedded in nanorods with diameters of 60-100nm were fabricated by inductively coupled plasma reactive ion etching with Cl-2/Ar plasma. The strong optical emission of the nanorods, observed by micro-photoluminescence measurement at 80 K, reveals a large blue shift of about 90meV and an increase in photoluminescence intensity density of more than 17-fold, compared with that of the as-grown wafer under the same excitation power density of 80W/cm(2). These nanostructures have a high potential for application in efficient GaN-based vertical cavity emitters.
Improving Light Output Power of the GaN-Based Vertical-Injection Light-Emitting Diodes by Mg+ Implanted Current Blocking Layer
(2009-05-01)
Tsai, Min-An
;
Yu, Peichen
;
Chen, J. R.
;
Huang, J. K.
;
Chiu, C. H.
A method for forming a current blocking layer (CBL) by ion implantation in GaN-based vertical-injection light-emitting diodes (VI-LEDs) was proposed. It was found that the use of CBL in VI-LEDs can effectively reduce the current crowding effect and enhance the light output power. The uniform emission intensity distribution of VI-LEDs with CBL was demonstrated by electroluminescence measurements. Experimental results show that the wall-plug efficiency was enhanced by 12.3% at an injection current of 20 mA, compared to that of VI-LEDs without CBL, and by 56.2% compared to that of conventional LEDs. The device simulation results reveal that the current path can be blocked by CBL, resulting in high light extraction efficiencies and large current densities within the effective emission region of active layers.
Analysis of influence of alkyl sources on deep levels in GaN by transient capacitance method
(1996-07-01)
Chen, JF
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Chen, NC
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Huang, WY
;
Lee, WI
;
Feng, MS
The transient capacitance method nas used to analyze GaN samples grown by low-pressure organometallic vapor phase epitaxy (OMVPE) with triethylgallium (TEGa) or trimethylgallium (TMGa) as the alkyl source. Two deep levels at 1.10 and 1.27 eV were observed in the TMGa sample, while a deep level at 0.60 eV was observed in the TEGa sample. Using light illumination, levels deeper than those above were investigated in TEGa and TMGa samples.
Study on GaN micro-rod growth by nature patterned sapphire substrate
(2009)
Hsu, S. C.
;
Tu, P. M.
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Chen, I. R.
;
Cheng, Y. J.
;
光電工程學系
In this study, we Investigated the kinetics and etched morphology on sapphire substrate by mixing acid solutions We developed different etching conditions to produce various etching morphology patterns on sapphire surface Then, GaN micro-rod embedded with quantum wells (QWs) were grown on the patterned sapphire surface The cathode luminescence (CL) images of these QW embedded micro-rods have shown great crystal quality.
化學機械研磨在氧化鋁及氮化鎵上的應用研究
(2000)
施敏
;
SZE SIMON MIN
;
交通大學電子工程系

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