Browsing by Author "Jou, MJ"

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A finiteness theorem for maximal independent sets
(1996)
Jou, MJ
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Chang, GJ
;
Lin, C
;
Ma, TH
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應用數學系
Denote by mi(G) the number of maximal independent sets of G. This paper studies the set S(k) of all graphs G with mi(G) = k and without isolated vertices (except G congruent to K-1) or duplicated vertices. We determine S(1), S(2), and S(3) and prove that V(G) less than or equal to 2(k-1) + k - 2 for any G in S(k) and k greater than or equal to 2; consequently, S(k) is finite for any k.
AlGaInP light-emitting diodes with stripe patterned omni-directional reflector
(2006-02-01)
Lee, YJ
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Lu, TC
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Kuo, HC
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Wang, SC
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Liou, MJ
An n-side-up AlGaInP-based light-emitting diode (LED) with a stripe-patterned omni-directional reflector (ODR) was fabricated by adopting the adhesive-layer bonding scheme. Comparing to the conventional ODR LED, the stripe-patterned ODR LED significantly enhanced the output power with an only slight higher forward voltage. This improvement was analyzed by the scanning near-field optical microscope (SNOM) and could be attributable to the geometrical shape of stripe patterns that redirects the guided light towards to the escaping cone of the LED surface. The optimized dimension of stripe patterns was also calculated by simply modeling a LED dice with a stripe-patterned ODR structure, according to optical ray-tracing method.
Algorithmic aspects of counting independent sets
(2002-10-01)
Jou, MJ
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Chang, GJ
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應用數學系
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Department of Applied Mathematics
This paper studied the problems of counting independent sets, maximal independent sets, and maximum independent sets of a graph from an algorithmic point of view. In particular, we present linear-time algorithms for these problems in trees and unicyclic graphs.
Enhancing the output power of GaN-based LEDs grown on wet-etched patterned sapphire substrates
(2006-05-01)
Lee, YJ
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Hwang, JM
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Hsu, TC
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Hsieh, MH
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Jou, MJ
GaN-based light-emitting diodes (LEDs) with emitting wavelength of 450 nm were grown on patterned sapphire substrates (PSSs) fabricated by chemical wet etching. The crystallography-etched facet was {1-102} R-plane with a 57 degrees against {001} C-axis and had superior capability for enhancing light extraction efficiency. The light output power of the PSS LED was 1.15 times higher than that of the conventional LED at an injection current of 20 mA. The output power and external quantum efficiency were estimated to be 9 mW and 16.4%, respectively. The improvement was attributed not only to geometrical shapes of {1-102} crystallography-etched facets that efficiently scatter the guided light to find escape cones, but also to dislocation density reduction by adopting the PSS growth scheme.
GaN-based LEDs with Al-deposited V-shaped sapphire facet mirror
(2006-03-01)
Lee, YJ
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Hwang, JM
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Hsu, TC
;
Hsieh, MH
;
Jou, MJ
A GaN-based light-emitting diodes (LEDs) with V-shaped sapphire facet reflector was fabricated using the double transferred scheme and sapphire chemical wet etching. The {1-102} R-plane V-shaped facet reflector with a 57 degrees against {0001} C-axis has the superior capability for enhancing the light extraction efficiency. The light output power of the V-shaped sapphire facet reflector LED was 1.4 times higher than that of a flat reflector LED at an injection current of 20 mA. The significant improvement is attributable to the geometrical shape of sapphire facet reflector that efficiently redirects the guided light inside the chip toward to the top escape-cone of the LED surface.
High brightness AlGaInP-based light emitting diodes by adopting the stripe-patterned omni-directional reflector
(2006-02-01)
Lee, YJ
;
Lu, TC
;
Kuo, HC
;
Wang, SC
;
Liou, MJ
An n-side-up AlGaInP-based LED operating at a wavelength of 630 nm with a stripe-patterned omni-directional reflector (ODR) was fabricated by adopting the adhesive-layer bonding scheme. It is demonstrated that the periodic and geometrical shape of the stripe-patterned array improves the light extraction efficiency by increasing the extraction of guided light. Compared to the conventional ODR LED, the stripe-patterned ODR LED significantly enhanced the output power and with only a slightly higher forward voltage. This improvement was analysed by the scanning near-field optical microscope (SNOM) and the optimized dimension of stripe patterns was also calculated on the basis of a Monte Carlo ray tracing simulation. According to the above analysis, the increase of light extraction could not only be attributed to the geometrical shape of the stripe patterns that redirect the trapped light towards the top-escaping cone of the LED surface but also to the repetitive stripe-patterned array of diffracting elements that effectively diffract the guided light outside the LED surface. Moreover, the optimized dimension of the stripe pattern is 3 mu m wide, 2 mu m deep and spaced 3 mu m apart, which coincides with experimental results.
Improvement in light-output efficiency of AlGaInP LEDs fabricated on stripe patterned epitaxy
(2005-12-01)
Lee, YJ
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Tseng, HC
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Kuo, HC
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Wang, SC
;
Chang, CW
Quaternary AlGaInP light-emitting diodes (LEDs) operating at a wavelength of 630 nm with a stripe-patterned omni-directional reflector (ODR) were fabricated. It is demonstrated that the geometrical shape of stripe-patterned structure improves the light extraction efficiency by increasing the extraction of guided light. The optical and electrical characteristics of stripe-patterned ODR LEDs are presented and compared to typical ODR and distributed Bragg reflector (DBR) LEDs with the same epitaxial structure and emitting wavelength. It is shown that the output power of the stripe-patterned ODR LED exceeds that of the typical ODR and DBR LEDs by a factor of 1.15 and 2 times, respectively, and with an acceptable forward voltage of about 2.2 V.
Improvement in light-output efficiency of near-ultraviolet InGaN-GaN LEDs fabricated on stripe patterned sapphire substrate
(2005)
Lee, YJ
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Hsu, TC
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Kuo, HC
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Wang, SC
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Yang, YL
The output power of GaN-based near ultraviolet stripe patterned sapphire substrate (PSS) LEDs was 20% higher than that of the conventional LEDs. The possible mechanism of this enhancement will be discussed in this report.
Improvement in light-output efficiency of near-ultraviolet InGaN-GaN LEDs fabricated on stripe patterned sapphire substrates
(2005-09-25)
Lee, YJ
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Hsu, TC
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Kuo, HC
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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.
Increasing the extraction efficiency of AlGaInP LEDs via n-side surface roughening
(2005-11-01)
Lee, YJ
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Kuo, HC
;
Wang, SC
;
Hsu, TC
;
Hsieh, MH
An n-side-up AlGaInP-based light-emitting diode (LED) with a triangle-like surface morphology was fabricated using the adhesive layer bonding technique, followed by wet etching to roughen the surface. The light output power of the roughened-surface LED was 1.6 times higher than that of a flat-surface LED at an injection current of 20 mA, i.e., a significant improvement attributed to the ability of the roughened surface to not only reduce the internal reflection between the rear mirror system and the semiconductor-air interface, but also to effectively scatter the light outside the LED device.
Maximal independent sets in graphs with at most one cycle
(1997-11-27)
Jou, MJ
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Chang, GJ
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應用數學系
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Department of Applied Mathematics
In this paper, we determine the largest number of maximal independent sets among all connected graphs of order n, which contain at most one cycle. We also characterize those extremal graphs achieving this maximum value. As a consequence, the corresponding results for graphs with at most one cycle but not necessarily connected are also given.
Novel approach to enhance the optical property in AlGaAs and InGaAlP by natural ordering during growth
(1996)
Chin, A
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Lin, BC
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Gu, GL
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Hsieh, KY
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Jou, MJ
Long range alloy ordering is observed by cross-sectional TEM in both (111)A and (111)B AlGaAs. We have measured a 31 meV photoluminescence (PL) peak energy red shift of (111)A and (111)B Al0.30Ga0.70As to that of (100), while the PL integrated intensity in (111)A and (111)B is near an order of magnitude larger than that of (100). The ordering effect is reduced at a high growth temperature of 700 degrees C and the best PL linewidth of 17 and 3 meV are obtained in (111)A Al0.40Ga0.60As and (111)B Al0.30Ga0.70As, respectively. In the In0.6Ga0.4P/InGaAlP MQW, similar ordering related PL peak energy red shift of 37 meV and similar to 2 times enhanced PL integrated intensity are observed for 0 degrees sample to that of 15 degrees.
Reactive ion etching of compound semiconductors grown by MOCVD technique with BCl3/SF6/Ar mixtures
(1995)
Chang, KM
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Tsai, JY
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Yeh, CB
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Yeh, TH
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Wang, SW
Survey on counting maximal independent sets
(1998)
Chang, GJ
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Jou, MJ
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應用數學系
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Department of Applied Mathematics
Erdos and Moser raised the problem of determining the largest number of maximal independent sets of a general graph of order n and those graphs achieving this maximum value. This problem was solved by Erdos, and later Moon and Moser. Two decades later, the problem was extensively studied for various classes of graphs, including trees, forests, (connected) graphs with at most one cycle, bipartite graphs, connected graphs, k-connected graphs and (connected) triangle-free graphs. This paper surveys results on this and related problems.
The number of maximal independent sets in connected triangle-free graphs
(1999-02-28)
Chang, GJ
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Jou, MJ
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應用數學系
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Department of Applied Mathematics
Erdos and Moser raised the problem of determining the largest number of maximal independent sets of a general graph G of order n and those graphs achieving this largest number. This problem was solved by Erdos, and later Moon and Moser. It then was extensively studied for various classes of graphs, including trees, forests, (connected) graphs with at most one cycle, bipartite graphs, connected graphs, k-connected graphs and triangle-free graphs. This paper studies the problem for connected triangle-free graphs. In particular, we prove that every connected triangle-free graph of order n greater than or equal to 22 has at most 5 . 2((n-6)/2) (respectively, 2((n-1)/2)) maximal independent sets if n is even (respectively, odd). Extremal graphs achieving this maximum value are also characterized. (C) 1999 Elsevier Science B.V. All rights reserved.
The number of maximum independent sets in graphs
(2000-12-01)
Jou, MJ
;
Chang, GJ
;
應用數學系
;
Department of Applied Mathematics
In this paper, we study the problem of determining the largest number of maximum independent sets of a graph of order n. Solutions to this problem are given for various classes of graphs, including general graphs, trees, forests, (connected) graphs with at most one cycle, connected graphs and triangle-free graphs. Extremal graphs achieving the maximum values are also given.
Thermal stability study of Ni/Ta n-GaN Schottky contacts
(2002-01-28)
Chen, GL
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Chang, FC
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Shen, KC
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Ou, J
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Chen, WH
The Schottky behavior of Ni/Ta and Ni contacts on n-GaN was investigated under various annealing conditions by current-voltage measurements. It is found that with the addition of Ta between the Ni layer and the GaN substrate the thermal stability properties of devices can be significantly improved. Experimental results indicate that a high quality Ni/Ta n-GaN Schottky diode with an ideality factor and barrier height of 1.16 and 1.24 eV, respectively, can be obtained under 1 h annealing, at 700 degreesC. (C) 2002 American Institute of Physics.