Browsing by Author "Yao, HH"

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Aluminum incorporation into AlGaN grown by low-pressure metal organic vapor phase epitaxy
(2006-05-15)
Huang, GS
;
Yao, HH
;
Lu, TC
;
Kuo, HC
;
Wang, SC
Aluminum (Al) incorporation in AlxGa1-xN films grown by low-pressure metal organic vapor phase epitaxy using trimethylaluminum (TMAl) and trimethylgallium as group III precursors has been systematically studied. The solid phase Al composition of the AlxGa1-xN films varied nonlinearly with the Al gas phase composition. The incorporation kinetics of AlxGa1-xN alloy has been analyzed by using an adsorption-trapping model. Two parameters were used to characterize the properties of Al incorporation, i.e., the capture radius and the adsorption time of Al atoms. An exponential function of the Al composition of the AlxGa1-xN films versus the TMAl gas flow rate was obtained. It was demonstrated that the adsorption time of the Al atom was larger than the growth time of one atomic layer. The effects of ammonia flow rate, crystal growth rate, and growth temperature on the adsorption parameters were also discussed. (c) 2006 American Institute of Physics.
An optically pumped blue GaN-based vertical-cavity surface emitting laser employing AIN/GaN and Ta2O5/NO2 distributed bragg reflectors
(2005)
Kao, CC
;
Yao, HH
;
Peng, YC
;
Lu, TC
;
Kuo, HC
The laser action of GaN-based VCSEL with 3-lambda cavity and hybrid DBR mirrors, consisting of AlN/GaN and Ta2O5/SiO2 DBR was achieved under the optical pumping at room temperature. The laser emits 448nm blue wavelength with a linewidth of 0.25nm above threshold.
Characteristics of stable emission GaN-based resonant-cavity light-emitting diodes
(2004-01-19)
Lin, CF
;
Yao, HH
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Lu, JW
;
Hsieh, YL
;
Kuo, HC
The resonant-cavity light-emitting diode (RC-LED) structure was grown by MOCVD. The structure of RC-LED consisted of a 3lambda InGaN/GaN MQW LED cavity between the top TiO2/SiO2 DBR (81.7%, reflectance) and the bottom AlN/GaN DBR (90.4%) stack. A stable 410 nm emission peak and a low thermally induced red-shift effect (0.12 nm/kA/cm(2)) were measured by varying the injection current density. The light output power of the full RC-LED device was three times higher than the RC-LED without top TiO2/SiO2 DBR layers under 600 A/cm(2) inject current density. The narrow line width of 7.4 nm, emission peak localization at 410 nm, and three times higher output power were caused by the resonance effect in this vertical cavity structure. (C) 2003 Published by Elsevier B.V.
Crack-free GaN/AlN distributed Bragg reflectors incorporated with GaN/AlN superlattices grown by metalorganic chemical vapor deposition
(2006-02-06)
Huang, GS
;
Lu, TC
;
Yao, HH
;
Kuo, HC
;
Wang, SC
A crack-free GaN/AlN distributed Bragg reflector (DBR) incorporated with GaN/AlN superlattice (SL) layers was grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition. Three sets of half-wave layers consisting of 5.5 periods of GaN/AlN SL layers and GaN layer were inserted in every five pairs of the 20 pair GaN/AlN DBR structure to suppress the crack generation. The grown GaN/AlN DBRs with SL insertion layers showed no observable cracks in the structure and achieved high peak reflectivity of 97% at 399 nm with a stop band width of 14 nm. Based on the x-ray analysis, the reduction in the in-plane tensile stress in the DBR structure with insertion of SL layers could be responsible for the suppression of crack formation and achievement of high reflectivity. (c) 2006 American Institute of Physics.
Fabrication and performance of blue GaN-based vertical-cavity surface emitting laser employing AlN/GaN and Ta2O5/SiO2 distributed Bragg reflector
(2005-08-22)
Kao, CC
;
Peng, YC
;
Yao, HH
;
Tsai, JY
;
Chang, YH
GaN-based vertical-cavity surface emitting laser with 3 lambda cavity and hybrid mirrors, consisting of the 25 pairs AlN/GaN dielectric Bragg reflector and the 8 pairs Ta2O5/SiO2, was fabricated. The laser action was achieved under the optical pumping at room temperature with a threshold pumping energy density of about 53 mJ/cm(2). The laser emits 448 nm blue wavelength with a linewidth of 0.25 nm and the laser beam has a degree of polarization of about 84%. (c) 2005 American Institute of Physics.
High-speed modulation of InGaAs : Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-mu m emission wavelength
(2005-03-01)
Kuo, HC
;
Chang, YH
;
Yao, HH
;
Chang, YA
;
Lai, FI
1.27-mum InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than similar to35% as the temperature raised from room temperature to 70 degreesC. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured,to be 10.7 GHz with modulation current efficiency factor (MCEF) of similar to5.25 GHz/(mA)(1/2). These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25 degreesC to 70 degreesC.
Influence of dislocation density on photoluminescence intensity of GaN
(2005-05-01)
Falth, JF
;
Gurusinghe, MN
;
Liu, XY
;
Andersson, TG
;
Ivanov, IG
The influence of dislocation density on photoluminescence intensity is investigated experimentally and compared to a model. GaN samples were grown by molecular beam epitaxy and metal-organic chemical vapour deposition. Different growth parameters and thicknesses of the layers resulted in different dislocation densities. The threading dislocation density, measured by atomic force microscopy, scanning electron microscopy and X-ray diffraction, covered a range from 5 x 10(8) to 3 x 10(10) cm(-2). Carrier concentration was measured by capacitance-voltage-, and Hall effect measurements and photoluminescence at 2 K was recorded. A model which accounts for the photoluminescence intensity as a function of dislocation density and carrier concentration in GaN is developed. The model shows good agreement with experimental results for typical GaN dislocation densities, 5 x 10(8)-1 x 10(10) cm(-2), and carrier concentrations 4 x 10(16)-1 x 10(18) cm(-3). © 2005 Elsevier B.V. All rights reserved.
InGaN self-assembled quantum dots grown by metal-organic chemical vapour deposition with growth interruption
(2006-03-28)
Yao, HH
;
Lu, TC
;
Huang, GS
;
Chen, CY
;
Liang, WD
Self-assembled InGaN quantum dots (QDs) were grown by metal-organic chemical vapour deposition with growth interruption at low V/III ratio and low growth temperature on sapphire substrates. The effects of the interruption time on the morphological and optical properties of InGaN QDs were studied. The results show that the growth interruption can modify the dimension and distribution of InGaN QDs, and cause the QD emission wavelength to blue shift with increasing interruption time. A density of InGaN QDs of 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 can be obtained by using a growth interruption time of 60 s.
MOCVD growth of AlN/GaN DBR structure under various ambient conditions
(2003)
Yao, HH
;
Lin, CF
;
Wang, SC
;
光電工程學系
;
Department of Photonics
High reflectivity AlN/GaN DBR structures were grown by MOCVD under three ambient gas conditions during the AlN layer growth. Highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442 nm was obtained under pure N2 gas ambient growth condition. The center wavelength of the DBR structures blue-shifted to 418 nm and 371 nm and the peak reflectivity also showed a reduction to 92% and 79% under the ambient gas conditions of a N2/H2 mixture and pure H2 respectively. Surface roughness showed slight increase from 8 nm to 12 nm, and the groove depth shows an increase from 25 nm to 60 nm with increasing the H2 ambient gas ratio. TEM results showed that AlN grown rate was reduction with the increasing H2 content in the ambient gas. The simulation result indicated that optical loss of AlN layers was increased from 450 cm-1 to 1850 cm-1 with the increasing H2 content in the ambient gas.
MOCVD growth of AlN/GaN DBR structures under various ambient conditions
(2004-02-15)
Yao, HH
;
Lin, CF
;
Kuo, HC
;
Wang, SC
;
光電工程學系
The high-reflectivity AlN/GaN distributed Bragg reflector (DBR) structures were realized by metal organic chemical vapor deposition (MOCVD) growth under pure N-2 ambient for AlN epilayer growth. The highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442 nm was obtained. For the DBR structure with AIN layer grown under mixture of N-2/H-2 and pure H-2 conditions, the center wavelength was blue-shifted to 418 and 371 nm and the peak reflectivity also showed a reduction to 92% and 79%, respectively. The stopband width also decreases with increasing H-2 contents. The surface roughness and the grain size of the grown DBR structures showed an increase with increasing the H-2 ambient gas ratio. For realization of a high reflectivity and broad bandwidth of AlN/ GaN DBR by using the MOCVD growth method, the pure N-2d ambient gas for growth of AIN layer should be preferable and optimal condition. (C) 2003 Elsevier B.V. All rights reserved.
MOCVD growth of highly strained InGaAs : Sb-GaAs-GaAsP quantum well vertical cavity surface-emitting lasers with 1.27 mu m emission
(2004-12-10)
Kuo, HC
;
Yao, HH
;
Chang, YH
;
Chang, YA
;
Tsai, MY
1.27mum InGaAs:Sb-GaAs-GaAsP vertical cavity surface-emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition (MOCVD) with superior performance. The threshold current changes between 1.8 and 1.1 mA and the slope efficiency drops below similar to35% when the temperature is raised from room temperature to 70degreesC. With only 5 mA of bias current, the 3 dB modulation frequency response is measured to be 8.36 GHz which is suitable for 10Gb/s operation. The maximal bandwidth is estimated to 10.7GHz with modulation current efficiency factor MCEF) of similar to5.25GHz/(mA)(1/2). The results of InGaAs:Sb-GaAs-GaAsP VCSELs can reach a performance level comparable to GalnAsN VCSELs with better thermal stability and should be considered as a very promising candidate for 1.3 mum commercial applications. (C) 2004 Elsevier B.V. All rights reserved.
Room-temperature operation of optically pumped blue-violet GaN-based vertical-cavity surface-emitting lasers fabricated by laser lift-off
(2006-04-01)
Chu, JT
;
Lu, TC
;
Yao, HH
;
Kao, CC
;
Liang, WD
Room-temperature optically pumped GaN-based vertical-cavity surface- emitting lasers (VCSELs) were demonstrated by laser lift-off. A VCSEL was fabricated by combining a GaN-based cavity with two dielectric distributed Bragg reflectors: SiO2/TiO2 and SiO2/Ta2O5. The Q factor of the VCSEL is 518 indicating a good interfacial layer quality of the structure. The laser emits blue-violet wavelength light at 414 nm under optical pumping at room temperature with a threshold pumping energy of 270 nJ. The laser emission has a narrow linewidth of 0.25 nm and a degree of polarization of 70%. The laser emission patterns clearly indicate a vertical lasing action of the VCSEL.
The lasing characteristics of GaN-based vertical-cavity surface-emitting laser with AlN-GaN and Ta2O5-SiO2 distributed Bragg reflectors
(2006-03-01)
Kao, CC
;
Lu, TC
;
Huang, HW
;
Chu, JT
;
Peng, YC
The characteristics of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with 25 pairs AIN-GaN distributed Bragg reflector (DBR) and eight pairs Ta2O5-SiO2 DBR was investigated and analyzed under the optical pumping at room temperature. The GaN-based VCSEL emits a blue wavelength at 448 nm with a linewidth of 0.17 nm with a near-field emission spot diameter of about 3 mu m. The laser beam has a near linear polarization with a degree of polarization of about 84%. The laser shows a high spontaneous emission coupling efficiency of about 5 x 10(-2) and a high characteristic temperature of about 244 K.