Browsing by Author "Kao, Chih-Chiang"

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Crs
(2008)
Lu, Tien-Chang
;
Kao, Tsung-Ting
;
Chen, Shih-Wei
;
Kao, Chih-Chiang
;
Lin, Li-Fan
We report fabrication of GaN-based two-dimensional surface emitting photonic-crystal lasers and successful demonstration of lasing action at room temperature with the emission wavelength at 424.3 nm and a low threshold pumping energy density of 3.5 mJ/cm(2). (c) 2008 Optical Society of America
CW lasing of current injection blue GaN-based vertical cavity surface emitting laser
(2008-04-07)
Lu, Tien-Chang
;
Kao, Chih-Chiang
;
Kuo, Hao-Chung
;
Huang, Gen-Sheng
;
Wang, Shing-Chung
Here, we report the cw laser operation of electrically pumped GaN-based vertical cavity surface emitting laser (VCSEL). The GaN-based VCSEL has a ten-pair InGaN/GaN multiple quantum well active layer embedded in a GaN hybrid microcavity of 5 lambda optical thickness with two high reflectivity mirrors provided by an epitaxially grown AlN/GaN distributed Bragg reflector (DBR) and a Ta(2)O(5)/SiO(2) dielectric DBR. cw laser action was achieved at a threshold injection current of 1.4 mA at 77 K. The laser emitted a blue wavelength at 462 nm with a narrow linewidth of about 0.15 nm. The laser beam has a divergence angle of about 11.7 degrees with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5x10(-2) was measured. (C) 2008 American Institute of Physics.
Emission characteristics of optically pumped GaN-based vertical-cavity surface-emitting lasers
(2006-09-18)
Chu, Jung-Tang
;
Lu, Tien-Chang
;
You, Min
;
Su, Bor-Jye
;
Kao, Chih-Chiang
The laser emission characteristics of a GaN-based vertical-cavity surface-emitting laser with two dielectric distributed Bragg reflectors were investigated under optically pumped operation at room temperature. The laser emitted wavelength at 415.9 nm with an emission linewidth of 0.25 nm and threshold pumping energy of 270 nJ. The laser has a high characteristic temperature of about 278 K and high spontaneous emission coupling factor of 10(-2). The laser emission showed single and multiple spot emission patterns with spectral and spatial variations under different pumping conditions. (c) 2006 American Institute of Physics.
GaN-based high-Q vertical-cavity light-emitting diodes
(2007-10-01)
Lu, Tien-Chang
;
Kao, Tsung-Ting
;
Kao, Chih-Chiang
;
Chu, Jung-Tang
;
Yeh, Kang-Fan
We report a fabrication and demonstration of a GaN-based high-Q vertical-cavity light-emitting diode (VCLED). The GaN VCLED is composed of a 25-pair high-reflectivity (98%) GaN/AlN distributed Bragg reflector (DBR), an eight-pair SiO2/Ta2O5 dielectric DBR (99%), and a three-A optical thickness InGaN/GaN active region. It shows a very narrow linewidth of 0.52 nm, corresponding to a cavity Q-value of 895 at a driving current of 10 mA and a dominant emission peak wavelength at 465.3 nm. In addition, this VCLED emission linewidth continues to decrease with an increasing injection current, suggesting a possible realization of GaN-based vertical-cavity surface emitting lasers.
GaN-based two-dimensional surface-emitting photonic crystal lasers with AlN/GaN distributed Bragg reflector
(2008-01-07)
Lu, Tien-Chang
;
Chen, Shih-Wei
;
Lin, Li-Fan
;
Kao, Tsung-Ting
;
Kao, Chih-Chiang
GaN-based two-dimensional (2D) surface-emitting photonic crystal (PC) lasers with AlN/GaN distributed Bragg reflectors are fabricated and demonstrated. The lasing threshold energy density is about 3.5 mJ/cm(2) per pulse under optical pumping at room temperature. Only one dominant emission wavelength of 424.3 nm with a narrow linewidth of 1.1 A above the threshold is observed. The laser emission covers whole circularly 2D PC patterns (50 mu m in diameter) with a small divergence angle. The lasing wavelength emitted from 2D PC lasers with different lattice constants occurs at the calculated band-edges provided by the PC patterns. The characteristics of large area, small divergence angle, and single mode emission from the GaN-based 2D surface-emitting PC lasers should be promising in high power blue-violet emitter applications.
Investigation of InGaN/GaN light emitting diodes with nano-roughened surface by excimer laser etching method
(2007-01-25)
Huang, Hung-Wen
;
Kao, Chih-Chiang
;
Chu, Jung-Tang
;
Wang, Wei-Chih
;
Lu, Tien-Chang
The InGaN/GaN light emitting diodes (LEDs) with a nano-roughened top p-GaN surface fabricated by using Ni nano-masks and laser etching methods were demonstrated and analyzed. The experiment results observed the maximum light output power of the InGaN/GaN LED with a nano-roughened top p-GaN surface etched with the laser energy of 300 mJ/cm(2) was 1.55 times higher than that of a conventional LED, and the wall-plug efficiency was enhanced 68% at 20 mA. The series resistance of InGaN/GaN LED was reduced by 32% by the increase in the contact area of the nano-roughened surface. (c) 2006 Elsevier B.V. All rights reserved.
Light-output enhancement of GaN-based light-emitting diodes by photoelectrochemical oxidation in H2O
(2006-09-01)
Lai, Fang-I
;
Chen, Wei-Yo
;
Kao, Chih-Chiang
;
Ku, Hao-Chung
;
Wang, Shing-Chung
The light output of GaN-based light-emitting diodes (LEDs) was improved by an oxide film being directly grown on the p-GaN surface utilizing photoelectrochemical (PEC) oxidation via H2O. The light outputs of the LEDs were enhanced by approximately 16 and 37% after 30 and 45 min PEC oxidation, respectively, compared to those of a conventional LED at 20 mA, and the PEC oxidized LEDs exhibited almost the same dynamic resistance (R = dV/dI) as conventional LEDs without PEC oxidation. Atomic force microscopy (AFM) data show that the roughness of the interface between oxide film and p-GaN increases with oxidation time. In addition, the oxide film on the top surface of the GaN-based LED caused the antireflection effect and the changes of the surface effective refractive indices consequently increased the critical angle and in caused more light to be emitted from the GaN-based LED.
Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching
(2007-05-01)
Kao, Chih-Chiang
;
Kuo, H. C.
;
Yeh, K. F.
;
Chu, J. T.
;
Peng, W. L.
In this paper, we report the fabrication and characteristics of nano-roughened GaN laser lift-off (LLO) light-emitting diodes (LEDs) with different scale surface roughness. The surface roughness of devices was controlled by inductively coupled plasma reactive inn etching. Using this fabrication method to form nanoscaled roughness, the electrical property was almost not degraded. Furthermore, the light-output power and wall-plug efficiency of LLO LED could be both significantly enhanced about two times using this simple method.
Optically pumped GaN-based vertical cavity surface emitting lasers: Technology and characteristics
(2007-08-01)
Wang, Shing-Chung
;
Lu, Tien-Chang
;
Kao, Chih-Chiang
;
Chu, Jong-Tang
;
Huang, Gen-Sheng
We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AIN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed bv Ta2O5/SiO and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240K was measured, and a distinct spatially inhomooeneous emission pattern was observed.
Rapid self-assembly of Ni nanodots on Si substrate covered by a less-adhesive and heat-accumulated SiO2 layers
(2006-08-14)
Lin, Gong-Ru
;
Kuo, Hao-Chung
;
Lin, Huang-Shen
;
Kao, Chih-Chiang
;
光電工程學系
Rapid self-aggregation of Ni nanodots on Si substrate covered with a thin SiO2 buffered layer is investigated. The Ni nanodots can hardly self-aggregate on highly heat-dissipated Si substrate with a thermal conductivity of 148 W/m K. Adding a 200-A-thick SiO2 buffer with an ultralow thermal conductivity of 1.35 W/m K prevents the formation of NiSi2 compounds, enhances the heat accumulation, and releases the adhesion at Ni/Si interface, which greatly accelerates the self-assembly of Ni nanodots. Dense Ni nanodots with size and density of 30 nm and 7x10(10) cm(-2), respectively, can be formatted after rapid thermal annealing at 850 degrees C for 22 s. (c) 2006 American Institute of Physics.
Self-assembled Ni nanodot on SiO(2) film-a novel reactive ion etching mask for Si nanopillar formation on Si substrate
(2006-01-01)
Lin, Huang-Shen
;
Kao, Chih-Chiang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
;
Lin, Gong-Ru
By rapid thermal annealing the Ni film evaporated on thin SiO(2) layer covered Si substrate, we have successfully demonstrated the self-aggregation of two-dimensional randomized Ni nano-dots on Si wafer. The thin oxide layer prevents the formation of NiSi(2) compounds and facilitates the self-assembly of Ni nanodots from retaining the thermal power on SiO(2) layer. This greatly shrinks the annealing time required for metallic nanodot formation from > 10 min to < 30 sec. With the advantage of the self-assemble Ni/SiO(2) nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of < 50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICPRIE) procedure. After removing Ni dots and the SiO(2) film on the Si substrate, both the visible and near infrared photoluminescence from the Si nano-pillar sample were observed and analyzed.
Self-assembled Ni nanodot on SiO2 film-a novel reactive ion etching mask for Si nanopillar formation on Si substrate
(2006-01-01)
Lin, Huang-Shen
;
Kao, Chih-Chiang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
;
Lin, Gong-Ru
By rapid thermal annealing the Ni film evaporated on thin SiO2 layer covered Si substrate, we have successfully demonstrated the self-aggregation of two-dimensional randomized Ni nano-dots on Si wafer. The thin oxide layer prevents the formation of NiSi2 compounds and facilitates the self-assembly of Ni nanodots from retaining the thermal power on SiO2 layer. This greatly shrinks the annealing time required for metallic nanodot formation from > 10 min to < 30 sec. With the advantage of the self-assemble Ni/SiO2 nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of < 50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICPRIE) procedure. After removing Ni dots and the SiO2 film on the Si substrate, both the visible and near infrared photoluminescence from the Si nano-pillar sample were observed and analyzed.
The Characteristics of a High-Q GaN Micro-cavity Light Emitting Diodes
(2007)
Kao, Chih-Chiang
;
Lu, Tien-Chang
;
Kao, Tsung-Ting
;
Lin, Li-Fan
;
Kuo, Hao-Chung
We report the characteristics of a GaN high-Q micro-cavity light-emitting diode (MCLED). The GaN MCLED showed a very narrow linewidth of 0,52 nm at 10 mA and a dominant emission peak wavelength at 465.3 nm. (C)2007 Optical Society of America
The Lasing Action of GaN-based Two-Dimensional Surface-emitting Photonic Crystal Lasers
(2008)
Lu, Tien-Chang
;
Kao, Tsung-Ting
;
Chen, Shih-Wei
;
Kao, Chih-Chiang
;
Lin, Li-Fan
We report fabrication of GaN-based two-dimensional surface emitting photonic-crystal lasers and successful demonstration of lasing action at room temperature with the emission wavelength at 424.3 nm and a low threshold pumping energy density of 3.5 mJ/cm(2). (c) 2008 Optical Society of America