Browsing by Author "Lee, WH"

Now showing 1 - 20 of 30

A comparative study of Ar and H-2 as carrier gases for the growth of SiC films on Si(100) by electron cyclotron resonance chemical vapor deposition at low temperature
(2001-11-01)
Lee, WH
;
Lin, JC
;
Lee, C
;
Cheng, HC
;
Yew, TR
Electron cyclotron resonance chemical vapor deposition (ECR-CVD) of SiC films from silane and methane gas mixtures at low temperature has been investigated using two different carrier gases, namely, argon and hydrogen. The results obtained are compared. The chemical composition and crystalline microstructure were investigated by Fourier transform infrared spectroscopy (FTIR) and cross-sectional transmission electron microscopy (XTEM), respectively. The results indicate that the carrier gases have a greater influence on the film composition and microstructure as compared to the growth parameters like pressure, power and flow ratio. The deposition mechanism which controls the film characteristics is also presented. (C) 2001 Elsevier Science B.V. All rights reserved.
A high-temperature thermodynamic model for metalorganic vapor phase epitaxial growth of InGaN
(1999-09-01)
Ou, J
;
Pan, YC
;
Lee, WH
;
Shu, CK
;
Lin, HC
A thermodynamic analysis tailored with a high-temperature parameter was performed for metalorganic vapor phase epitaxial (MOVPE) growth of InxGa1-xN alloys. Accordingly, a series of InGaN samples were prepared under various input In flow rates and growth temperatures. Theoretical results indicate that the In solid concentration tends to increase with increasing In flow rate and with decreasing temperature, whereas the metal droplets form more easily on the surface at lower growth temperatures and higher In fluxes, which are in good agreement with our experimental data.
A novel architecture for multilane-free-flow electronic-toll-collection systems in the millimeter-wave range
(2005-09-01)
Shieh, WY
;
Lee, WH
;
Tung, SL
;
Ho, CD
;
資訊工程學系
An architecture for simultaneously performing multitarget tracking and multidata communication suitable for millimeter-wave multilane-free-flow electronic-toll-collection (ETC) systems is presented. This architecture combines the idea of frequency multiplexing in communication systems and the technique of target tracking in the pulse-Doppler radar. For target tracking, we make use of pulse ranging by the aid of pulse compression and fine target-direction determination by amplitude comparison to obtain high resolution in the radial direction (downrange), as well as both lateral directions (cross ranges). This architecture can be utilized for both active and passive onboard-unit (OBU) systems. Another important advantage of this architecture is that it can easily identify the passing vehicles not equipped with an OBU. This will activate some subsequent enforcement activities against the violation vehicles.
Characteristics of optical properties of the interrupt growth method on InGaN/GaN MQW structures
(2000)
Lin, CF
;
Shu, CK
;
Lee, WH
;
Wen, TC
;
Chu, CF
The growth method and material properties of InGaN/GaN multiple quantum well (MQW) structures were studied in this experiment. The InGaN/GaN-MQW structure were deposited above the 2 mum-thick high quality GaN layers (with background carrier concentration was about 3.2 x 10(16) cm(-3)) on Al2O3 substrates. The interrupt growth time was 10 sec between GaN barrier layer and InGaN well growth at 690 degreesC. The stronger intensity and sharper photoluminescence (PL) spectra was observed from the interrupt growth MQW structures. The mean deviation of the PL peak position was lower than 1% by using the interrupt growth MQW structures at difference growth temperature. The PL spectra was become broaden and weaker by reducing the interrupt time during InGaN/GaN growth. The thickness of one pair InGaN/GaN was also identified by DCX-ray measurement and the growth rate InGaN layer was also calculated in this experiment.
Deposition of polycrystalline beta-SiC films on Si substrates at room temperature
(1997-01-13)
Cheng, KL
;
Cheng, HC
;
Lee, WH
;
Lee, CP
;
Liu, CC
Polycrystalline beta-SiC, with grain size up to 1500 Angstrom, has been room-temperature-deposited on Si substrates by electron cyclotron resonance chemical vapor deposition. Microwave power and the hydrogen carrier gas are the key parameters to lower the deposition temperature. According to the results of the cross-sectional transmission electron microscopy, the grain size appeared to be in the same scale as that deposited at 500 degrees C while a large amount of plasma-induced defects were observed in the Si substrate for the room-temperature-deposited samples. Hence, a CH4-plasma treatment prior to the beta-SiC film growth was adopted, forming a SiC-like interfacial layer to suppress the substrate damages. (C) 1997 American Institute of Physics.
Development of dielectric composite with X7R characteristic
(2001)
Lee, WH
;
Ou, KH
;
Tsai, TL
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A dielectric composite having K-value in excess of 10000 with Y5R characteristics (-55 similar to +125 degreesC, +/- 15%) has been successfully developed which in corporate two (Ba, Ca)(Ti,Zr)O-3-based ceramic with different Curie temperature as the principal components. A stacking alternately technique during screen printing and a usual cofiring with inner electrode technique are utilised to prepared this kind of multilayer product. In this study, it is determined that a proportion of high-T-c and low T-c materials and location of their Curie temperature could control and improve the change of the dielectric constant (K) over a temperature range from -55 to +125 degreesC.
Effect of glass additions on the sintering behaviors and electrical microwave properties of BaO-Nd2O3-Sm2O3-TiO2 ceramics
(2004-03-01)
Chang, LC
;
Chiou, BS
;
Lee, WH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of Al2O3-doped silica glass (AS-glass) addition on the structure and dielectric properties of the BaO-Nd2O3-Sm2O3-TiO2 (BNST) microwave materials was investigated. This BNST material has a dielectric constant (k) of 80 and a quality factor (Q x f) of 6000 GHz when sintered at 1350degreesC for 2 h. Both the microstructure and the microwave dielectric characteristics were determined as a function of the sintering temperature and glass content. A Q x fas high as 8700 GHz was achieved in ceramics added with 20 wt% glass, however, the k value drops to 30. The high Q x f value is attributed to the improved densification of the dielectric when glass is added. Results of X-ray diffraction experiments indicate that glass addition enhances the growth in the longitudinal direction of the columnar crystal and a preferred (002) orientation. The presence of columnar structure plays an important role in the improvement of the microwave dielectric properties. (C) 2004 Kluwer Academic Publishers.
Effects of A/B cation ratio on the microstructure and lifetime of (Ba1-xCax)(z)(Ti0.99-y ZryMn0.01)O-3 (BCTZM) sintered in reducing atmosphere
(2000-03-01)
Lee, WH
;
Tseng, TY
;
Hennings, D
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Microstructure and dielectric properties of (Ba1-xCax)(z)(Ti0.99-yZry Mn-0.01)O-3 (BCTZM) with various cation ratios (A/B) sintered in reducing atmosphere and then annealed to reoxidize the ceramic bodies were investigated. With decreasing A/B cation ratio, concurrent with the grain size reduction, the insulation resistance and lifetime of the BCTZM are both increased. The degradation of insulation resistance is closely related to oxygen partial pressure used during annealing and the resulting microstructure of the ceramics. Within the same volume, the specimen with fine grain size provides more grain boundaries, in comparison to large grain size specimens, which helps in providing an efficient diffusion pathway for oxygen during annealing. The result of oxidation of the Mn, that is, a change in the valence state of Mn from Mn+2 to Mn+3 is confirmed from thermogravimetric analysis and electron paramagnetic resonance analysis.
Effects of calcination temperature and A/B ratio on the dielectric properties of (Ba,Ca)(Ti,Zr,Mn)O-3 for multilayer ceramic capacitors with nickel electrodes
(2000-06-01)
Lee, WH
;
Tseng, TY
;
Hennings, DFK
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical performance of multilayer ceramic capacitors (MLCCs) with Ni inner electrodes, made from (Ba,Ca)-(Ti,Zr,Mn)O-3 (BCTZM), is closely related to the calcination temperature and the A/B ratio of the powder. For materials showing A/B = 1.000, the lifetime, the breakdown voltage, and the RC increase with higher calcination temperatures. No significant effect of the calcination temperature on RC and lifetime was found for materials showing A/B = 0.991, The isoelectric point of BCTZM is shifted toward higher pH values when the calcination temperature is decreased. The above results are attributed to the colloidal stability of aqueous BCTZM suspensions and the resulting green density of powder compacts.
Effects of ceramic processing parameters on the microstructure and dielectric properties of (Ba1-xCax)(Ti0.99-y, ZryMn0.01)O-3 sintered in a reducing atmosphere
(2001-02-01)
Lee, WH
;
Tseng, TY
;
Hennings, D
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of A/B ratio, sintering temperature, and oxygen partial pressure on microstructure and ceramic dielectric properties of 1 mol % MnO2 doped (Ba,Ca)(Ti,Zr,)O-3 sintered in a reducing atmosphere were investigated. Microstructure is found to be closely related to processing parameters. With decreasing A/B ratio, decreasing oxygen partial pressure and increasing sintering temperature, grain growth is enhanced. Concurrent with the grain size reduction, the crystal structure transformed from tetragonal to pseudocubic at room temperature and the dielectric constant, the dissipation factor and Curie point all decreased. However, the effects of grain size give a marked discrepancy on breakdown. The effect of A/B ratio and sintering temperature both suggest that breakdown voltage is decreased with increasing grain size. However, the breakdown voltage in relation to grain size by changing the oxygen partial pressure seems to show no significant difference. (C) 2001 Kluwer Academic Publishers.
Effects of CH4/SiH4 flow ratio and microwave power on the growth of beta-SiC on Si by ECR-CVD using CH4/SiH4/Ar at 200 degrees C
(2002-02-22)
Lee, WH
;
Lin, JC
;
Lee, C
;
Cheng, HC
;
Yew, TR
The effects of CH4/SiH4 flow ratio and microwave power on the formation of SiC at 200 degreesC by electron cyclotron resonance chemical vapor deposition is investigated. When the CH4/SiH4 flow ratio is varied from 0.5 to 10, crystalline phase of films vary from polycrystalline silicon to polycrystalline P-SiC and finally to amorphous silicon carbide. However, as the microwave power increases from 300 to 1500 W. the film microstructure changes from polycrystalline Si to amorphous SiC. and finally to polycrystalline beta-SiC. The deposition mechanism which controls the film characteristics is also presented. (C) 2002 Elsevier Science B.V. All rights reserved.
Gallium K-edge EXAFS study of GaN : Mg films
(2000)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lin, WC
;
Shu, CK
Ga K-edge extended X-ray absorption fine structure (EXAFS) measurement was employed to investigate the local structure of GaN:Mg films grown by metalorganic vapor phase epitaxy (MOVPE) with various Cp,Mg dopant flow rates using both in-plane and out-of-plane polarization modes of X-ray. The near edge absorption spectra were found to depend on X-ray polarization strongly for undoped GaN sample and weakly to minutely for heavily Mg-doped and amorphous films. The results indicate Mg incorporation modifies the local structure around the absorber Ga atom and, hence, alters the molecular orbital electron transition of GaN sample. EXAFS analysis showed both vacancy and Mg-interstitial defects contribute to the reduction of coordination numbers along the hexagonal c-axis of GaN:Mg film.
Gallium K-edge x-ray absorption study on Mg-doped GaN
(2001-01-01)
Pan, YC
;
Wang, SF
;
Lee, WH
;
Lee, MC
;
Chen, WK
Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples. (C) 2001 American Institute of Physics.
Growth temperature reduction for isoelectronic As-doped GaN
(2003-03-01)
Lee, WH
;
Huang, HY
;
Chen, WC
;
Lee, CF
;
Chen, WK
As-doped GaN films were grown at different temperatures by atmospheric metalorganic chemical vapor deposition. A higher electron Hall mobility, narrower line width in photoluminescence, and longer spatial correlation length of the filmes were obtainable at low growth temperatures compared to undoped GaN grown at the same temperatures as a result of isoelectronic As-doping.
High precision, low cost mask for deep x-ray lithography
(1998-02-01)
Shew, BY
;
Cheng, Y
;
Shih, WP
;
Lu, M
;
Lee, WH
The precision of transferred patterns are highly dependent on the quality of the mask in deep x-ray lithography. Many parameters, such as the critical energy of the synchrotron light, beamline optics and even the microstructure to be exposed should be considered in mask design. In this paper, the design rules and the boundary conditions for deep x-ray mask are discussed in general. The method of making a precision, multilayer mask using UV lithography technique is also described.
High precision, low cost mask for deep x-ray lithography
(1998-02-01)
Shew, BY
;
Cheng, Y
;
Shih, WP
;
Lu, M
;
Lee, WH
The precision of transferred patterns are highly dependent on the quality of the mask in deep x-ray lithography. Many parameters, such as the critical energy of the synchrotron light, beamline optics and even the microstructure to be exposed should be considered in mask design. In this paper, the design rules and the boundary conditions for deep x-ray mask are discussed in general. The method of making a precision, multilayer mask using UV lithography technique is also described.
Influence of sapphire nitridation on properties of indium nitride prepared by metalorganic vapor phase epitaxy
(1999-02-01)
Pan, YC
;
Lee, WH
;
Shu, CK
;
Lin, HC
;
Chiang, CI
Indium nitride films have been successfully grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) using TMIn and NH3 as source precursors. Experimental results indicated that pregrowth treatments, such as buffer layer growth, nitridation temperature and nitridation duration have dramatic effects on the growth of the InN films. For films nitridated at 1,000 degrees C for 40 min without any buffer layer growth, we obtained an InN film quality with Hall mobility, carrier concentration and line width of Raman E-2 mode of 270 cm(2)/V.s, 5 x 10(19) cm(-3) and 4.5 cm(-1), respectively, which is among the best quality ever reported for such type of film grown by MOVPE.
Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition
(2000-10-30)
Huang, HY
;
Lin, WC
;
Lee, WH
;
Shu, CK
;
Liao, KC
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor-acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I-2) transition in undoped GaN increases with temperature as T-1.5. However, the I-2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. (C) 2000 American Institute of Physics. [S0003-6951(00)01941-0].
Low temperature deposited highly-conductive N-type SiC thin films
(1997)
Cheng, KL
;
Cheng, HC
;
Lee, WH
;
Lee, C
;
Yew, TR
Low-temperature deposited highly-conductive SiC films has long been a goal for many researchers involved in hetero-junction bipolar transistor, thin-film transistor, solar cell...etc. Were in this paper, we study the influences of the diluted PH3 now rates on SiC film quality as well as electrical properties. PH+ was determined from residual gas analyzer to be the main dopant source. Phosphorous atoms will play a role of enhancing the SiC grain growth and resulting in a smaller film growth rate. Carrier concentrations increase monotonically with the diluted PH; now rates. While Hall mobility first increases than decreases with it due to a combination effect of the impurity scattering and a film quality improvement which dominates when the 1% PH3/H-2 flow rate is above or below 40 seem, respectively.
Luminescence intensity reduction in Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2001-04-01)
Shu, CK
;
Chen, HH
;
Lee, WH
;
Pan, YC
;
Huang, HY
Photoluminescence dynamic responses of a heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy have been investigated. As the probe power density increased from 2.5 to 925 W/cm(2), a Mg-related emission band shifted from 2.82 to 3.16 eV revealing characteristics of donor-acceptor pair recombination. The intensity evolution also showed slow decay that suggests the metastable emission behavior. A simple potential barrier model was proposed to occur between the Mg related deep levels and common Mg acceptor level, which impedes electron relaxation and thus slows down the luminescence decay. From the variation of decay time constant with temperature. a barrier energy was deduced to be about 69 meV which is very close to the electrical result of 68 meV.