Browsing by Author "Chung, HM"

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An analytical approach for the fast design of high-power waveguide windows
(2003-02-01)
Lin, MC
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Chung, HM
;
Burke, A
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電子物理學系
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Department of Electrophysics
An analytical approach is presented to achieve the fast design of high-power waveguide windows. The analytical calculation is compared with the result of numerical simulation via the finite-element code high frequency structure simulator and the experiments of W-band waveguide windows performed at the Stanford Linear Accelerator Center (SLAC), Stanford University, Stanford, CA. The closed form has been carried out to enhance the accuracy and efficiency, and the exact calculation agrees with the experimental results and the numerical simulation very well. (C) 2002 Elsevier Science B.V. All rights reserved.
Characteristics of deep levels in As-implanted GaN films
(2002-09-02)
Lee, L
;
Lee, WC
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Chung, HM
;
Lee, MC
;
Chen, WH
Hall, current-voltage and deep level transient spectroscopy measurements were used to characterize the electric properties of n-type GaN films implanted with As atoms. After 800 degreesC thermal annealing for 60 min, one additional deep level located at E-C-0.766 eV was found in the films. We presume this induced trap is an arsenic-related point defect, most likely antisite in nature. (C) 2002 American Institute of Physics.
Characteristics of p-type GaN films doped with isoelectronic indium atoms
(2002-12-01)
Chang, FC
;
Shen, KC
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Chung, HM
;
Lee, MC
;
Chen, WH
The method of isoelectronic doping, is employed to prepare p-type GaN films using metalorganic chemical vapor deposition. With the addition of In atoms, the film surface becomes much smoother, and the corresponding hole concentration and resistivity are also improved, to 8.7 x 10(17) cm(-3) and similar to 1 Omega-cm, respectively. More interestingly, it is found that an ohmic I-V characteristic can be obtained in such types of films without any dehydrogenation treatment.
Comparative study of Schottky diode characteristics in Ni, Ta and Ni/Ta metal contact schemes on n-GaN
(2001-07-01)
Chen, GL
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Chang, FC
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Chuang, WC
;
Chung, HM
;
Shen, KC
We have reported current-voltage characteristics of Ta/- and Ni/Ta/n-GaN Schottky diodes under various thermal treatments. Experimental data indicate that the electrical characteristics of Ni/Ta diodes are controlled by the interfacial properties of the Ta and GaN heterointerface for the as-deposited samples and strongly affected by the presence of an oxide layer (Ta2O5) in those high-temperature-annealed diodes. In regard to Ta/Ni diodes, probably because of thermal stability and wide-bandgap properties of tantalum oxide, dramatic improvement in Schottky diode performance was resulted after annealing at high temperatures. The corresponding barrier height and ideality factor values can reach 1.17 cV and 1.09, respectively, even at an annealing temperature of 800 degreesC.
Decimalization, trading costs, and information transmission between ETFs and index futures
(2006-02-01)
Chou, RK
;
Chung, HM
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資訊管理與財務金融系註：原資管所+財金所
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Department of Information Management and Finance
The impact of changes in trading costs, due to decimalization, on informed trading and speed of information transmission between exchange-traded funds (ETFs) and their corresponding index futures is examined. ETFs began to trade in decimals on January 29, 2001, and index futures continued to trade in their original tick sizes. The focus is on whether the decrease in the minimum tick size of ETFs influences the relative performances of these two types of index instruments in the price-discovery process. It is found that for ETFs, the trading activity increases, but the market depth drops significantly after decimalization. The spreads for ETFs generally decrease, but the adverse selection component of ETF spreads increases. Furthermore, after decimalization, ETFs start to lead index futures in the price-discovery process and its share of information also increases. Although index futures still assume a dominant role in information discovery, the information content of the ETFs' prices improves significantly after decimalization. (c) 2006 Wiley Periodicals, Inc.
Dependence of deep level concentrations on ammonia flow rate in n-type GaN films
(2002-08-01)
Lee, L
;
Chang, FC
;
Chung, HM
;
Lee, MC
;
Chen, WH
Deep level transient spectroscoppy was used to characterize the deep levels of GaN films grown with various V/III ratios using metalorganic vapor phase epitaxy. Two prominent defects, located at E(C)-0.569 +/- 0.003 and E(C)-1.013 +/- 0.091 eV, were detected in this study. When the NH(3) flow rate was increased, we observed a slight increase in trap concentration of the E(C)-0.569 eV defect and a significant increase at E(C)-1.013 eV. Although a high V/III seems necessary for obtaining good quality GaN film, our results indicate that, if the ammonia is in excessive supply, it may generate a large number of E(C)-1.013 eV deep level defects, which deteriorate the film quality - which should be avoided with special care.
Detecting mutual fund timing ability using the threshold model
(2005-10-20)
Chou, PH
;
Chung, HM
;
Sun, EY
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管理科學系
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資訊管理與財務金融系註：原資管所+財金所
This paper proposes a new method based on threshold regression to test mutual fund market-timing abilities. The traditional Henriksson and Merton model is shown to represent only a special case within the proposed model. The potential bias of using the traditional model is demonstrated and it is argued that the proposed model provides more accurate inferences on the market-timing effects or mutual funds. The empirical results for a set of randomly-selected US mutual funds indicate the superior performance of the proposed method in detecting the market-timing ability.
Investor protection and the liquidity of cross-listed securities: Evidence from the ADR market
(2006-05-01)
Chung, HM
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Using 'American depository receipt' (ADR) data on various countries, this paper sets out to investigate the relationship between investor protection and firm liquidity. Since weak investor protection leads to greater expropriation by managers, and thus greater asymmetric information costs, liquidity providers will incur relatively higher costs and will therefore offer higher bid-ask spreads. The empirical results demonstrate that the liquidity costs of poor investor protection were more significant during the period of the Asian financial crisis when the expected agency costs were particularly severe. This issue is further analyzed by investigating whether there is any evidence of increases in the vulnerability of ADRs of firms operating in countries with relatively poor investor protection mechanisms during periods of financial crisis. (c) 2005 Elsevier B.V. All rights reserved.
Long-term photocapacitance decay behavior in undoped GaN
(2001-10-01)
Chung, HM
;
Pan, YC
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Chuang, WC
;
Chen, NC
;
Tsai, CC
We have measured the dynamic response of the photocapacitance of a Schottky diode made of an undoped GaN epilayer grown by metalorganic vapor phase epitaxy. The measurements were performed after the suspension of a white light for a specified "waiting" time, t. The results indicate that the capacitance exhibits a logarithmic function of t from which a time constant of approximately 34.5 s and a cross-sectional area of less than 2.89 x 10(-27) cm(2) were retrieved. These are interpreted as the characteristic time and the cross-sectional area of electron capture by the traps associated with dislocations formed in the epifilm, respectively.
Long-term photocapacitance decay behavior in undoped GaN
(2000)
Chung, HM
;
Pan, YC
;
Chung, WC
;
Chen, NC
;
Tsai, CC
We have employed the photocapacitance measurement to examine the physical properties of GaN Schottky diode made from the undoped epilayer grown by metalorganic vapor phase epitaxy. The resulted transient capacitance spectrum shows that the diode exhibits a characteristic of long-term logarithmic-type decaying behavior, which, we believe, is correlated closely to the linear arranged traps close to the core of the threading edge dislocations.
Price clustering in E-mini and floor-traded index futures
(2006-03-01)
Chung, HM
;
Chiang, SM
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
This article sets out to investigate price clustering in both the open-outcry (floor-traded) and electronically traded (E-mini) index futures markets of the DjlA, S&P 500, and NASDAQ-100 indices. The results show that although price clustering is ubiquitous in both the floor-traded and E-mini index futures markets, it nevertheless tends to be higher for open-outcry index futures, with the clustering in floor-traded NASDAQ-100 index futures demonstrating the highest level (97%) at zero digits. A significant increase was also found in price clustering in floor-traded index futures after the introduction of E-mini futures trading. The results tend to suggest that those trading mechanisms that involve higher levels of human participation, such as the open-outcry markets, may well lead to increased incidences of price clustering. (c) 2006 Wiley Periodicals, Inc.
Rapid thermal annealing effects on blue luminescence of As-implanted GaN
(2002-10-01)
Huang, HY
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Xiao, JQ
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Ku, CS
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Chung, HM
;
Chen, WK
Rapid thermal annealing effects on blue luminescence of As-implanted GaN grown by metalorganic vapor phases epitaxy were investigated by means of photoluminescence and photoluminescence excitation measurements. The locations of the As-implantation induced bands and the associated transition channels for the emission were determined to characterize the As-implanted GaN. After the rapid thermal annealing treatment, the deep As-related levels become more ready to be populated by photoexcitation at low temperature so that the new blue luminescence emission peak is enhanced significantly, whose activation energy is found to be 46 meV. (C) 2002 American Institute of Physics.
The dynamic relationship between the prices of ADRs and their underlying stocks: evidence from the threshold vector error correction model
(2005-11-10)
Chung, HM
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Ho, TW
;
Wei, LJ
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管理科學系
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資訊管理與財務金融系註：原資管所+財金所
This paper sets out to estimate the dynamic relationship that exists between the prices of ADRs and their underlying stocks, in both the short run and the long run, using a number of recent developments of the threshold cointegration framework. The empirical results support the notion of nonlinear mean reversion of the prices of ADRs and their underlying stocks.