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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.
Characteristics of stable emission GaN-based resonant-cavity light-emitting diodes
(2004-01-19)
Lin, CF
;
Yao, HH
;
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.
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.
Study of dry etching for GaN and InGaN-based laser structure using inductively coupled plasma reactive ion etching
(2004-03-25)
Kao, CC
;
Huang, HW
;
Tsai, JY
;
Yu, CC
;
Lin, CF
Dry etching of undoped, n-GaN, p-GaN and InGaN laser structure was investigated by inductively coupled plasmas reactive ion etching (ICP-RIE) using Ni mask. As Cl-2/Ar gas flow rates were fixed at 10/25 sccm, the etched surface roughness has the lowest value of 0.2 nm at constant ICP/bias power = 300/100 W and 5 mTorr chamber pressure for undoped GaN. The highest etching rate of 12,000 Angstrom/min for n-GaN was achieved at 30 mTorr, 300 W ICP, 100 W bias power using low Cl-2 flow rate (Cl-2/Ar = 10/25 sccm) gas mixtures. The surface roughness was dependent of bias power and chamber pressure, and shows a low root mean square (rms) roughness value of about I nm at 50 W of bias power for n-GaN and p-GaN. For etching of InGaN laser structure using high O-2 flow rate (Cl-2/Ar = 50/20 sccm) and low chamber pressure 5 mTorr, a smooth mirror-like facet of InGaN laser diode structure was obtained. Using these etching parameters, mirror-like facets can be obtained which can be used for the fabrication of nitride-based laser diodes. Moreover, at the fixed Cl-2/Ar flow rate of 10/25 sccm, ICP/bias power of 200/100 W and chamber pressure of 30 mTorr, the InGaN-based materials nanorods were fabricated with a density of about 10(8) cm(-2) and dimension of 50-100 nm. (C) 2004 Elsevier B.V. All rights reserved.
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.
Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls
(2005-01-01)
Kao, CC
;
Kuo, HC
;
Huang, HW
;
Chu, JT
;
Peng, YC
We successfully fabricated nitride-based light-emitting diodes (LEDs) with similar to 22degrees undercut sidewalls. The similar to 22degrees etching undercut sidewalls were achieved by controllable inductively coupled plasma reactive ion etching. With a 20-mA current injection, the output powers of the LED with similar to 22degrees undercut sidewalls and standard LED were 5.1 and 3 mW, respectively-a factor of 1.7 times enhancement. It was found that such undercut sidewalls could enhance the probability of escaping the photons outside from the LED in the near horizontal and in-plane directions. This simple and controllable method is beneficial to fabricate brighter LEDs.
Fabrication and micro-photoluminescence investigation of Mg-doped gallium nitride nanorods
(2005-04-01)
Chang, YH
;
Hsueh, TH
;
Lai, FI
;
Chang, CW
;
Yu, CC
High-density magnesium (Mg)-doped gallium nitride (GaN) nanorods were fabricated by inductively coupled plasma reactive ion etching from a GaN film and had a mean length of approximately 50nm. A large blue-shift was observed in the photoluminescence (PL) peak energy of Mg-doped GaN nanorods under HeCd laser (325 nm) excitation. The PL spectra of the nanorods show a typical donor-acceptor-pair (DAP) emission at approximately 3.0 eV with a large blue-shift compared to that of the Mg-doped GaN film. The blue-shift energy increases from 8 meV to 67 meV as the excitation intensity varies from 12 kW/cm(2) to 56 kW/cm(2). Possible reasons for the power dependence of the spectral shift in the PL emission energy are discussed.
Enhancement in light output of InGaN-based microhole array light-emitting diodes
(2005-06-01)
Hsueh, TH
;
Shen, JK
;
Huang, HW
;
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.
Improvement in light-output efficiency of near-ultraviolet InGaN-GaN LEDs fabricated on stripe patterned sapphire substrates
(2005-09-25)
Lee, YJ
;
Hsu, TC
;
Kuo, HC
;
Wang, SC
;
Yang, YL
InGaN/GaN multi-quantum wells near ultraviolet light-emitting diodes (LEDs) were fabricated on a patterned sapphire substrate (PSS) with parallel stripe along the (1100)(sapphire) direction by using low-pressure metal-organic chemical vapor deposition (MOCVD). The forward- and reverse-bias electrical characteristics of the stripe PSS LEDs are, respectively, similar and better than those of conventional LEDs on sapphire substrate. The output power of the epoxy package of stripe PSS LED was 20% higher than that of the conventional LEDs. The enhancement of output power is due not only to the reduction of dislocation density but also to the release of the guided light in LEDs by the geometric shape of the stripe PSS, according to the ray-tracing analysis. (c) 2005 Elsevier B.V. All rights reserved.
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.

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