Browsing by Author "Kao, CC"

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A novel method to improve VCSELs oxide-confined aperture uniformity using selective As+-implanted underlying layer
(2006-05-10)
Huang, HW
;
Kao, CC
;
Chang, YA
;
Kuo, HC
;
Laih, LH
We report the utilization of an selective As+-implanted underlying layer and regrowth method to enhance and control the wet thermal oxidation rate for 850 nm oxide-confined VCSEL. The oxidation rate of the As'-implanted device showed a four-fold increase over the non-implanted one at the As' dosage of 1 x 10(16) cm(-1) and the oxidation temperature of 400 degrees C. The 50 side-by-side As'-implanted oxide-confined VCSELs fabricated using the method achieved very uniform performance with a deviation in threshold current Of Delta I-th similar to 0.2 mA and slope-efficiency of Delta S.E. similar to 3%. Finally, we accumulated life test data for oxide-confined VCSELs with As'-implanted underlying layer up to 1000 h at 80 degrees C/15 mA. (c) 2005 Elsevier B.V. All rights reserved.
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.
Characterization of InGaN/GaN multiple quantum well nanorods fabricated by plasma etching with self-assembled nickel metal nanomasks
(2005-04-01)
Hsueh, TH
;
Huang, HW
;
Kao, CC
;
Chang, YH
;
Ou-Yang, MC
High-density (3.0 x 1010 cm (-2)) InGaN/GaN Multiple quantum well (MQW) nanorods were fabricated from an as-grown bulk light-emitting diode structure by inductively coupled plasma dry etching with self-assembled nickel metal nanomasks. The self-assembled nickel metal nanomasks were formed by rapid thermal annealing of a nickel metal film at 850 degrees C for 1 min. The influence of the thicknesses of the Ni metal film on the dimensions and density of the nanorods was also investigated. The structural and optical properties of the InGaN/GaN MQW nanorods were established using field emission scanning electron microscopy, transmission electron microscopy and photoluminescence measurements. The diameters and heights of nanorods were estimated to be 60 to 100nm and more than 0.28 mu m, respectively. The peak emission wavelength of the nanorods showed a blue shift of 5.1 nm from that of the as-grown bulk. An enhancement by a factor of 5 in photoluminescence intensity of the nanorods compared with that of the as-grown bulk was observed. The blue shift is attributed to strain relaxation in the wells after dry etching, the quantum confinement effect, or a combination of the two, which results in the enhancement of emission intensity.
Effect of different n-electrode patterns on optical characteristics of large-area p-side down InGaN light-emitting diodes fabricated by laser lift-off
(2005)
Chu, JT
;
Liang, WD
;
Kao, CC
;
Huang, HW
;
Chu, CF
Large-area (1000x1000 gm) p-side down InGaN light-emitting diodes (LEDs) have been fabricated by laser lift-off (LLO) technique. The p-side down LEDs with different geometric patterns of n-electrode were fabricated to investigate electrode pattern-dependent optical characteristics. Current crowding effect was first observed in in the p-side down InGaN LLO-LEDs. The LEDs with well designed n-electrode shows a uniform distribution of light-emitting pattern and higher out put power due to uniform current spreading and minimization of thermal effect. The output power saturation induced by current crowding in the LEDs with simplest geometric n-electrode was demonstrated. In absent of transparent contact layer for current spreading, the n-electrode pattern has remarkable influence on the current distribution and consequently the light output power of the large-area p-side down LEDs.
Effect of rapid thermal annealing on beryllium implanted p-type GaN
(2004-03-25)
Huang, HW
;
Kao, CC
;
Tsai, JY
;
Yu, CC
;
Chu, CF
We report the results of rapid thermal annealing (RTA) effect on beryllium implanted in situ activated p-type GaN samples and investigate the ramping and isothermal annealing effect of RTA process for these samples. It is found that the optimum RTA condition is at the temperature of 1100 degreesC for 15 s. Furthermore, with equal total isothermal time of 60 s, we compared the multiple step annealing (MSA) at 1100 degreesC for four periods with single step annealing (SSA) for one period at the same annealing temperature of 1100 degreesC, and observed that the ramping effect with MSA could repair Be-related complex defect, and one time, long period isothermal annealing effect with SSA seems to induce much more defect. It seems that the multiple step annealing is more effective and induce less defect than single step annealing for Be-implanted in situ activated p-type GaN samples. (C) 2004 Elsevier B.V. All rights reserved.
Effects of different n-electrode patterns on optical characteristics of large-area p-side-down InGaN light-emitting diodes fabricated by laser lift-off
(2005-11-01)
Chu, JT
;
Kao, CC
;
Huang, HW
;
Liang, WD
;
Chu, CF
Large-area p-side-down InGaN light-emitting diodes (LEDs) 1000 x 1000 mu m(2) in size have been fabricated by laser lift-off (LLO). The p-side-down LEDs with different geometric patterns of n-electrodes were fabricated to investigate electrode pattern-dependent optical characteristics. The current crowding effect was observed in the large-area p-side-down InGaN LLO-LEDs. A LED with a well-designed n-electrode pattern shows a uniform distribution of light emission and a higher output power due to uniform current spreading. The output power saturation induced by the current crowding effect was investigated. In the absence of a transparent contact layer for current spreading, the n-electrode pattern has a marked influence on the current distribution and the consequent light output power of the large-area p-side-down LEDs.
Efficient UV photoluminescence from monodispersed secondary ZnO colloidal spheres synthesized by sol-gel method
(2005-04-15)
Cheng, HM
;
Hsu, HC
;
Chen, SL
;
Wu, WT
;
Kao, CC
ZnO colloidal spheres were synthesized by sol-gel method with a narrow size distribution. We controlled the size of the spheres during the secondary reaction with various amounts of primary reaction supernatant. The optimized condition of ZnO powders with an average diameter of 185 nm was obtained for structure analysis and study of optical properties. Transmission electron microscopy and X-ray diffraction reveal that the spheres are polycrystalline in the pure wurtzite phase. Markedly enhanced near-band-edge ultraviolet pbotoluminescence and significantly reduced defect-related visible emission were also observed. We attribute this observation to the localized bound excitons with high density of defect states. In addition, broad yellow emission and green emission were observed when the powders were post-annealed at 500 degrees C in air ambience. The origins of the defect-induced visible emissions are attributed to oxygen interstitials and oxygen vacancies. (c) 2005 Elsevier B.V. All rights reserved.
Enhanced light output in InGaN-based light-emitting diodes with onmidirectional one-dimensional photonic crystals
(2006-03-01)
Lin, CH
;
Tsai, JY
;
Kao, CC
;
Kuo, HC
;
Yu, CC
We have Successfully designed and fabricated GaN-based light-emitting diodes (LEDs) containing an omnidirectional one-dimensional photonic crystal (ID PC). The ID PC is composed of alternatively stacked TiO2 and SiO2 layers designed to possess a photonic band gap (PBG) within the blue regime of interest. With the same multiple quantum well (MQW) emission peak at approximately 450 nm and a driving Current of 20 mA, the light output powers of the LED with and without the ID PC are approximately 11.7 and 6.5 mW, respectively. The enhancement in light extraction of our LED with ID PC demonstrates that a property designed omnidirectional ID PC can have a higher reflectance and a wider reflection angle than a conventional distributed Bragg reflector (DBR). Our work shows promising potential for the enhancement of output powers of commercial light emitting devices.
Enhanced light output in InGaN/GaN light emitting diodes with excimer laser etching surfaces
(2006-04-01)
Huang, HW
;
Chu, JT
;
Kao, CC
;
Hsueh, TH
;
Lu, TC
The InGaN/GaN light-emitting diode (LED) with a top p-GaN surface nanoroughened using Ni nanomasks and laser etching has been fabricated. The light output power of the InGaN/GaN LED with a nanoroughened top p-GaN surface is 1.55-fold that of a conventional LED. The series resistance of InGaN/GaN LED was reduced by 32% due to the increase in the contact area of the nanoroughened surface.
Enhanced light output of an InGaN/GaN light emitting diode with a nano-roughened p-GaN surface
(2005-09-01)
Huang, HW
;
Chu, JT
;
Kao, CC
;
Hseuh, TH
;
Lu, TC
This investigation describes the development of an InGaN/GaN light emitting diode (LED) with a nano-roughened top p-GaN surface using an Ni nano-mask and laser etching. The light output of the InGaN/GaN LED with a nano-roughened top p-GaN surface is 1.55 times that of a conventional LED, and the wall-plug efficiency is 68% higher at 20 mA. The series resistance of the InGaN/GaN LED was reduced by 32% by the increase in the contact area of the nano-roughened surface.
Enhancement in light output of InGaN-based microhole array light-emitting diodes
(2005-06-01)
Hsueh, TH
;
Shen, JK
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Huang, HW
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Chu, JY
;
Kao, CC
InGaN-based microhole array light-emitting diodes (LEDs) with hole diameters (d) of 3-15 mu m were fabricated using self-aligned etching. The effects of size on the device characteristics, including current density-voltage and light output-current density, were measured and compared with those of conventional broad-area (BA) LEDs fabricated from the same wafer. The electrical characteristics of the devices are similar to those of conventional BA LEDs. The light output from the microhole array LEDs increases with d up to 7 pm. However, the light output declined as d increased further, perhaps because of the combination of the enhancement in extraction efficiency caused by the large surface areas provided by the sidewalls and the decrease in area of light generation by holes in the microhole array LEDs. The ray tracing method was used with a two-dimensional model in TracePro software. The findings indicate that an optimal design can improve the light output efficiently of the microhole array LEDs.
Enhancement of light-output of GaN-based light-emitting diodes by bias-assisted photoelectrochemical oxidation of p-GaN in H2O
(2005)
Lai, FI
;
Chen, WY
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Kao, CC
;
Lin, CF
;
Kuo, HC
An enhancement of GaN-based LEDs light output using photoelectrochemical (PEC) oxidation method via H2O on the p-GaN surface was demonstrated. The output light was improved 37% after 45min PEC oxidation.
Fabrication and characteristics of GaN-based microcavity light-emitting diodes with high reflectivity AIN/GaN distributed Bragg reflectors
(2006-04-01)
Peng, YC
;
Kao, CC
;
Huang, HW
;
Chu, JT
;
Lu, TC
In this paper, we report a GaN-based microcavity light-emitting diode (MCLED) which is composed of 25 pairs of high-reflectivity GaN/AlN distributed Bragg reflector (DBR) and 6 pairs of ex-situ deposited SiO2/TiO2 dielectric mirrors. The electroluminescence peak of this structure matched well with the high reflectance area of the top and bottom DBRs, and shows a narrow emission of approximately 6.7 nm. The fabricated device also shows a more excellent performance on the stability of the emission peak wavelength while varying injection current density and operating temperature than a regular LED.
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.
Fabrication of GaN-based nanorod light emitting diodes using self-assemble nickel nano-mask and inductively coupled plasma reactive ion etching
(2004-10-25)
Huang, HW
;
Kao, CC
;
Hsueh, TH
;
Yu, CC
;
Lin, CF
We report a novel method to fabricate GaN-based nanorod light emitting diodes (LEDs) with controllable dimension and density using self-assemble nickel (Ni) and Ni/Si3N4 nano-masks and inductively coupled plasma reactive ion etching (ICP-RIE). Under the fixed Cl-2/Ar flow rate of 50/20 sccm. ICP/Bias power of 400/100 W and chamber pressure of 0.67 Pa, the GaN-based nanorod LEDs were fabricated with density of 2.2 x 10(9) to 3 x 10(10) cm(-2) and dimension of 150-60 nm by self assemble Ni nano-masks with various size. The size of Ni/Si3N4 nano-mask was control by the thickness Ni film ranging 150-50 Angstrom and rapid thermal annealing condition. The technique offers a controllable method of fabrication of GaN-based nanorod LEDs and should be applicable for fabrication of the others III-V nanoscale photonic and electronic devices. (C) 2004 Elsevier B.V. All rights reserved.
Fabrication of InGaN multi-quantum-well nanorod by Ni nano-mask
(2004)
Huang, HW
;
Hsueh, TH
;
Kao, CC
;
Chang, YH
;
Ou-Yang, M
Fabrication of large-area GaN-based light-emitting diodes on Cu substrate
(2005-04-01)
Chu, JT
;
Huang, HW
;
Kao, CC
;
Liang, WD
;
Lai, FI
A large-area GaN-based light-emitting diode (LED) 1000 x 1000 mu m(2) in size with a p-side down configuration was fabricated using wafer bonding and laser lift-off (LLO) techniques. The thin GaN LED was transferred onto a copper substrate without p peeling or cracks. The large-area LEDs showed a uniform light-emission pattern over entire defined mesa area without a transparent contact layer on the p-type GaN. The operating current of the large-area LEDs can be driven up to 1000 mA with continuously increasing light output-power. The light output-power is 240 mW with a driving current of 1000 mA. Large-area emission and high current operation make the LLO-LEDs applicable to high-power LED applications.
Fabrication of p-side down GaN vertical ligbt emitting diodes on copper substrates by laser lift-off
(2004)
Chu, JT
;
Kuo, HC
;
Kao, CC
;
Huang, HW
;
Chu, CF
The fabrication process and performance characteristics of the laser lift-off (LLO) GaN light emitting diodes (LEDs) were investigated. The LLO-GaN LEDs with 300 x 300 mum(2) on Cu show a nearly 4-fold increase in the light output power over the regular LLO-LEDs on the sapphire substrate. High operation current for the LLO-LEDs on Cu was also demonstrated. The large area-emission of 1000 x 1000 Pm 2 of p-side down GaN LLO-LEDs on Cu were fabricated. Further improvement of max light output are achieved. The LLO process should be applicable to other GaN-based light emitting devices in particular for those high light output power and high operation current devices. (C) 2004 WILEY-VCH Verlag GmbH & Co, KGaA, Weinheim.
Improvement of InGaN-GaN light-emitting diode performance with a nano-roughened p-GaN surface
(2005-05-01)
Huang, HW
;
Kao, CC
;
Chu, JI
;
Kuo, HC
;
Wang, SC
This investigation describes the development of InGaN-GaN light-emitting diode (LED) with a nano-roughened top p-GaN surface which uses Ni nano-mask and wet etching. The light output of the InGaN-GaN LED with a nano-roughened top p-GaN surface is 1.4 times that of a conventional LED, and wall-plug efficiency is 45% higher. The operating voltage of InGaN-GaN LED was reduced from 3.65 to 3.5 V at 20 mA and the series resistance was reduced by 20%. The light output is increased by the nano-roughening of the top p-GaN surface. The reduction in the series resistance can be attributed to the increase in the contact area of nano-roughened surface.
InGaN-based light-emitting diode with undercut side wall
(2004)
Kao, CC
;
Chu, JT
;
Huang, HW
;
Peng, YC
;
Yu, CC