Browsing by Author "Huang, G. S."

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Effect of growth conditions on the Al composition and quality of AlGaN film
(2007-01-15)
Huang, G. S.
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Yao, H. H.
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Kuo, H. C.
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Wang, S. C.
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光電工程學系
Effects of growth conditions on Al composition and quality of AlxGa1-xN epilayer grown by low-pressure matelorganic vapor phase epitaxy (MOVPE) have been investigated. The dependences of Al composition, growth rate and quality on the NH3 flow rate, TMAl flow rate and growth temperature were studied. The Al composition and quality of AlxGa1-xN film depend not only on the TMAl flow rate, but also on the NH3 flow rate and on the growth temperature. The Al composition of AlxGa1-xN film becomes saturated when the gas-phase composition TMAl/(TMAl + TMGa) increases to 0.4, while quality of AlxGa1-xN film becomes much worse. The Al composition of AlxGa1-xN film increases with increase in the NH3 flow rate. The quality of AlxGa1-xN epilayer is improved when the growth temperature increases. Possible Al incorporation mechanism is discussed. (c) 2006 Elsevier B.V. All rights reserved.
Effects of growth interruption time on InGaN/GaN quantum dots grown by metal organic chemical vapor deposition - art. no. 612102
(2006)
Yao, H. H.
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Huang, G. S.
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Lu, T. C.
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Chen, C. Y.
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Liang, W. D.
Wide-bandgap gallium nitride (GaN) quantum dot (QD) structure is attractive because it is a zero-dimensional (0-D) confinement structure and has many unique physical characteristics. We have successfully grown self-assembled InGaN QDs structure by metal organic chemical vapor deposition. A high quality GaN/sapphire template with a flat surface and the suitable growth condition including low growth temperature and low V/III ratio were used to grow InGaN QDs structure. The density of InGaN QDs is about 4.5 x 10(10) cm(-2) with an average lateral size of 11.5 nm and an average height of 1.6 nm. The effect of the interruption growth for InGaN QDs structure was systematic studied with the growth temperature of 660 degrees C. The surface morphology and optical property was measured by atomic forced microscopy and various temperature PL, respectively. The results indicated that as increasing interruption time from 30s to 120s, QDs area occupied on the surface above the wetting layer increases from 5.2% to 7.2%, and the In composition decreases from 25% to 21%. The results were discussed by considering the influences of ad-atom desorption and diffusion effect between wetting layer and InGaN QDs structure. Our results suggest that the interruption growth during an optimum time can modify the size of InGaN QDs and extend the emission wavelength to short wavelength, and at the same time improve the QD optical quality. Using this technique was feasible for formation of multi layer InGaN QDs structures and applicable for the fabrication of GaN-based light emitting devices.
Extreme Hyperlactatemia After Heart Transplantation: One Center's Experience
(2015-07-01)
Hsu, Y. C.
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Hsu, C. H.
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Huang, G. S.
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Lu, C. C.
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Wu, Z. F.
Introduction. Hyperlactatemia may occur early after cardiac surgery and is correlated with prognosis. This study was conducted to analyze the perioperative variables and postoperative outcomes among heart transplant recipients with extremely high lactate levels (>15 mmol/L). Methods. The single-center medical records of heart transplantation from June 2006 to May 2013 were retrospectively reviewed for patient characteristics, perioperative hemodynamic variables, arterial blood gas analysis data, and postoperative mortality. Results. Among 58 consecutive heart transplant recipients, lactate levels over the detectable upper limit (>15 mmol/L) were identified in 12 patients after intensive care unit admission, with peak time at 1.9 +/- 2.0 (range 0-6.1) hours. The maximal preoperative lactate level was 3.1 mmol/L, and most (11/12) postoperative lactate levels returned to <4 mmol/L at 27.5 +/- 12.8 hours after surgery (range 15-58, median 24), displaying a trend toward delayed extubation time in 10 recipients (P < .01). Blood glucose levels elevated significantly from preoperative 148.9 +/- 45.2 to 375.7 +/- 96.9 mg/dL at peak lactate level (P < .01). Four patients died in the ICU (range 5-32 days), 4 died after discharge (range 5-57 months), with 6 in total surviving over 1 year. Conclusion. Extreme hyperlactatemia commonly occurred early after heart transplantation and mostly recovered within 30 hours; however, with delayed extubation time after operation.
Fabrication of microcavity light-emitting diodes using highly reflective AlN-GaN and Ta2O5-SiO2 distributed Bragg mirrors
(2007-07-01)
Huang, G. S.
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Lu, T. C.
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Kuo, H. C.
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Wang, S. C.
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Chen, Hou-Guang
We report the fabrication of microcavity light-emitting diodes (MCLEDs) with high reflectivity and crack-free AIN-GaN distributed Bragg reflector (DBR). The 5 lambda microcavity structure consists of an n-type GaN, ten pairs InGaN-GaN multiple quantum wells and p-type GaN sandwiched between the hybrid cavity mode of an AIN-GaN and a Ta2O5-SiO2 DBR. The AIN-GaN DBR has 29 periods with insertion of six AIN-GaN superlattice layers showing a crack-free surface morphology and a high peak reflectivity of 99.4% with a stopband of 21 nm. The output power of MCLED is about 11 mu W at an injection current of 7 mA. The electroluminescence has a polarization property with a degree of polarization of about 51 %.
GaN/AlGaN active regions for terahertz quantum cascade lasers grown by low-pressure metal organic vapor deposition
(2007-01-01)
Huang, G. S.
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Lu, T. C.
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Yao, H. H.
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Kuo, H. C.
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Wang, S. C.
The GaN/AlGaN active regions for terahertz (THz) quantum cascade lasers were grown by metal organic chemical vapor deposition (MOCVD). The surface of the sample was characterized by atomic force microscopy (AFM). The structure of this sample was evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and cross-sectional TEM images showed that a well-controlled quantum cascade GaN/AlGaN layers could be prepared. Optical properties of the active region of a terahertz GaN/AlGaN have been investigated by Fourier transform infrared (FTIR) spectrometer. It was found that the frequency of E-1(LO) phonon decreased in quantum cascade GaN/AlGaN structures. The phonon frequency shift could be attributed to the effect of phonon zone folding. (c) 2006 Elsevier B.V. All rights reserved.
Hybrid nitride microcavity using crack-free highly reflective AlN/GaN and Ta2O5/SiO2 distributed Bragg mirrors
(2007-06-01)
Huang, G. S.
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Chen, Hou-Guang
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Chen, J.-R.
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Lu, T. C.
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Kuo, H. C.
We report the growth over 2 inch sapphire substrates of hybrid nitride-based microcavities using one crack-free highly reflective AIN/GaN distributed Bragg reflectors (DBRs) incorporated with AIN/GaN superlattice (SL) insertion layers and Ta2O5/SiO2 DBRs. The optical cavity is formed by a 5 lambda cavity consisting of n-type GaN, 10 pairs multiple quantum wells and p-type GaN sandwiched by AIN/GaN and Ta2O5/SiO2 DBRs. Reflectivity and photoluminescence measurements were carried out on these structures. A 29 periods AIN/GaN DBR incorporated with six AN/GaN superlattice insertion layers showed no observable cracks and achieved a peak reflectivity of 99.4% and a stopband of 21 run. Based on these high quality DBRs, the cavity mode is clearly resolved with a linewidth of 2.6 nm. These results demonstrate that the AIN/GaN system is very promising for the achievement of strong light-matter interaction and the fabrication of nitride-based vertical cavity surface emitting lasers. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Improvement of efficiency and ESD characteristics of ultraviolet light-emitting diodes by inserting AlGaN and SiN buffer layers
(2007-07-01)
Huang, G. S.
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Kuo, H. C.
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Lo, M. H.
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Lu, T. C.
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Tsai, J. Y.
We have studied the effect of the AlGaN insertion and SiN buffer layers of ultraviolet light-emitting diodes (UVLEDs) on efficiency and electrostatic discharge (ESD) characteristics of UVLEDs grown by metalorganic chemical vapor deposition. The etching pit density was reduced from 3.6 x 10(8) cm(-2) in conventional samples to 1.6 x 10(7) cm(-2) in UVLEDs grown with the AlGaN insertion layer and SiN buffer layer. During the ESD tests at the negative biases of 3000 V, the live percentage of UVLEDs increased from 67% in conventional samples to 86% in samples with AlGaN insertion layers and SiN buffer layers. In addition, the device shows a low leakage current of 1.1 x 10(-8) A at -5 V and the light output power was 70% higher than the conventional UVLEDs at an injection current of 20 mA. (c) 2007 Elsevier B.V. All rights reserved.
Nanoparticle-enhanced Magnetic Field Induces Apoptosis in Nematode
(2008)
Huang, G. S.
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Yeh, L. K.
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Chen, Y. C.
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材料科學與工程學系奈米科技碩博班
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Graduate Program of Nanotechnology , Department of Materials Science and Engineering
To investigate molecular consequence of magnetic field to C. elegans, Fe3O4 nanoparticles were incorporated into the culture media of C. elegans and the nematodes were grown under magnetic field for 4 days. For the expermental group, we observed a 30 to 50 percents reduction in the moving speed. However, only nematode at L4 stage exhibited this difference. To explore molecular mechanisms affected by this treatment, real-time RT-PCR was performed using primers specific to amplify 120 genes. Differential expression for genes belong to apoptosis was observed. Biochemical assay for Caspase 3 activity was performed. The magnetic field-treated nematode exhibited high levels of Caspase 3 activity consistent with real-time PRC. Fluorescence microscopy showed that apoptotic activity was associated with the Fe3O4 treatment. For further validation, a ced-3 mutant nematode under enhanced magnetic field showed less effect for the movement than wild-type. The current study indicated that nanoparticle-enhanced magnetic field induced apoptosis in nematode.
Observations on surface morphologies and dislocations of a-plane GaN grown by metal organic chemical vapor deposition
(2007)
Ko, T. S.
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Wang, T. C.
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Chen, H. G.
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Gao, R. C.
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Huang, G. S.
In this study, we grew non-polar a-plane GaN thin films on r-plane sapphire using a series of growth conditions by metal-organic chemical vapor deposition. The results showed that high temperature and low-pressure conditions benefited two-dimension growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best surface morphology with an excellent mean roughness of 10.5 angstrom was obtained. The different thickness AlN as a nucleation layer and the different delta/beta ratio were also considered. The results revealed that the surface morphology would get worse when the thickness of nucleation layer and delta/beta ratio were away from the values of optimal condition. The observation of transmission electronic microscopy shown the lowest density of threading dislocations was 1.85x10(10) /cm(2). (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Optically and electrically pumped GaN-based VCSELs
(2007)
Lu, T. C.
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Kao, C. C.
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Huang, G. S.
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Kuo, H. C.
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Wang, S. C.
We report the recent progress of GaN-based VCSELs with a hybrid cavity structure comprised an epitaxial AlN/GaN DBR with superlattice insertion layers, an InGaN/GaN MQW active region and a top dielectric DBR. The lasers achieved laser action under optical pumping at the room temperature with a narrow linewidth. The preliminary results of the electrically pumped VCSEL will also be presented.
Recent progress on GaN-based vertical cavity surface emitting lasers
(2007-01-01)
Lu, T. C.
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Kao, C. C.
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Huang, G. S.
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Kuo, H. C.
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Wang, S. C.
We report the recent progress of GaN-based VCSELs with two different laser structures. One is a hybrid cavity structure comprised an epitaxial AlN/GaN DBR, an InGaN/GaN MQW active region and a top dielectric DBR. Another is a dielectric cavity structure comprised an InGaN/GaN MQW layer sandwiched by two dielectric DBRs. Both lasers achieved laser action under optical pumping at the room temperature with narrow linewidth. The detailed characteristics of VCSELs will be reported. The status of the electrically pumped VCSEL will also be presented.
Recent progress on GaN-based vertical cavity surface emitting lasers - art. no. 67660G
(2007)
Lu, T. C.
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Kao, C. C.
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Huang, G. S.
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Kuo, H. C.
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Wang, S. C.
We report the recent progress of GaN-based VCSELs with two different laser structures. One is a hybrid cavity structure comprised an epitaxial AlN/GaN DBR, an InGaN/GaN MQW active region and a top dielectric DBR. Another is a dielectric cavity structure comprised an InGaN/GaN MQW layer sandwiched by two dielectric DBRs. Both lasers achieved laser action under optical pumping at the room temperature with narrow linewidth. The detailed characteristics of VCSELs will be reported. The status of the electrically pumped VCSEL will also be presented.
Study on optimal growth conditions of a-plane GaN grown on r-plane sapphire by metal-organic chemical vapor deposition
(2007-03-15)
Ko, T. S.
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Wang, T. C.
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Gao, R. C.
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Chen, H. G.
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Huang, G. S.
Non-polar a-plane (1 1 (2) over bar 0) GaN thin films were grown on r-plane (1 (1) over bar 0 2) sapphire substrates by metal-organic chemical vapor deposition. In order to obtain a-plane GaN films with better crystal quality and surface morphology, detailed comparisons between different growth conditions were investigated. The results showed that high-temperature and low-pressure conditions facilitating two-dimensional growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best mean roughness of the surface morphology was 10.5 angstrom. Various thickness values of AlN nucleation layers and the V/III ratios for growth of the a-plane GaN bulk were also studied to determine the best condition for obtaining a smooth surface morphology of the a-plane GaN layer. (c) 2007 Elsevier B.V. All rights reserved.