Browsing by Author "Wang, YK"

Now showing 1 - 13 of 13

Atomic force microscope study of GaN films grown by hydride vapor phase epitaxy
(1999)
Fang, HM
;
Wang, YK
;
Tsai, RY
;
Chu, CF
;
Wang, SC
We report the results of the investigation of the structural, surface morphological, and optical properties of GaN films grown by hydride vapor phase epitaxy. These films were grown on sapphire substrate with no intentional dopings. These as-grown GaN film samples with thickness ranging from 5.58 mu m to 14.9 mu m were investigated under room temperature conditions. The surface morphology of these films was investigated using an atomic force microscopy (AFM). The root mean square (RMS) values of surface roughness range from 0.281 nm to 0.133 nm. The thicker films show lower defect counts with a defect density of about 2 x 10(8) cm(-2). The structural property of these films was measured by double crystal X-ray diffraction (DC-XRD). The full width at half maximum (FWHM) of X-ray diffraction angle decreases as the film thickness increases with a lowest FWHM of about 265.5 arcsec. The optical properties of these films were investigated by photoluminescence (PL) measurement at room temperature. The results show a dominant near band-edge UV emission peak that increases with the film thickness with very weak yellow emission band.
Enhanced ferroelectric properties of Pb(Zr0.53Ti0.47)O-3 thin films on SrRuO3/Ru/SiO2/Si substrates
(2002-05-20)
Wang, YK
;
Tseng, TY
;
Lin, P
;
材料科學與工程學系
;
電子工程學系及電子研究所
Highly (110)-oriented Pb(Zr0.53Ti0.47)O-3 (PZT) films were deposited on SrRuO3 (SRO)/Ru/SiO2/Si substrates using a sol-gel method, in which SrRuO3 films were deposited at various substrate temperatures. The crystallinity of the PZT films was improved after the annealing process. The leakage current, dielectric constant, and polarization versus electric-field characteristics of PZT films were strongly dependent on the annealing and deposition temperatures of the SRO films. The 650 degreesC annealed PZT film grown on SRO has a leakage current of 9x10(-7) A/cm(2) at an applied field of 500 kV/cm, dielectric constant of 1306, remanent polarization (P-r) of 40.1 muC/cm(2) and coercive field (E-c) of 78.5 kV/cm at an applied voltage of 5 V. The PZT films indicated fatigue-free characteristics up to similar to1.0x10(12) switching cycles under 5 V bipolar pulse. (C) 2002 American Institute of Physics.
High etching rate of GaN films by KrF excimer laser
(2001-05-22)
Chu, CF
;
Lee, CK
;
Yu, CC
;
Wang, YK
;
Tasi, JY
A study of laser processing of gallium nitride (GaN) material is reported. A pulsed KrF excimer laser at 248 nm with 20-nsec pulse width and 1 Hz repetition rate is used to etch the GaN film. We establish the material etching parameters under different environmental conditions. By changing the pulsed energy at constant pulse numbers, ablation of GaN surface was observed at threshold laser fluence about 0.3 J cm(-2). Laser etching increase with reducing environment pressure. Al 1.0 J cm (-2) laser fluence, the etching fate is about 35 nm per pulse at atmosphere pressure and increases to 60 nm per pulse at low pressure. The etched depth also increases with increasing laser fluence. The surface morphology of the etched surface was also investigated. (C) 2001 Elsevier Science B.V. All rights reserved.
Hyper-Rayleigh scattering of thiophene-incorporated polyene chromophores with pi-configuration locking
(1997-08-15)
Hsu, CC
;
Shu, CF
;
Huang, TH
;
Wang, CH
;
Lin, JL
The hyper-Rayleigh scattering (HRS) technique is used to determine and compare the first hyperpolarizabilities (beta) of thiophene-incorporated polyene chromophores with and without a configuration locked trans-triene bridge, To ensure the purity of the HRS signal, special attention is paid to its dependence on the fundamental intensity and the spectral content of the scattered radiation including the two-photon absorption induced fluorescence. From the HRS results, it is found that the configuration-locked trans-triene bridge enhances the beta values of the chromophores studied, The beta-enhancement is more pronounced when the electron acceptor CHC(CN)(2) in the chromophores is replaced with C-2(CN)(3). (C) 1997 Elsevier Science B.V.
Influence of measuring environment on the electrical characteristics of pentacene-based thin film transistors
(2004-11-22)
Wang, YW
;
Cheng, HL
;
Wang, YK
;
Hu, TH
;
Ho, JC
This work concerns the electrical properties and carrier transport behavior of polycrystalline pentacene-based thin film transistors (TFTs) in air and high-vacuum environments. The transistor in a high vacuum outperforms that in air. The dependence of the field-effect mobility on the gate voltage and the drain voltage is considered. A potential barrier model is applied to estimate the trap density of the pentacene transistor. The determined trap density at the grain boundaries of the pentacene film in air exceeds that in a high vacuum. These results show that the increased trap concentration at the grain boundaries in ambient air limits carrier transport. (C) 2004 Elsevier B.V. All rights reserved.
Low-resistance ohmic contacts on p-type GaN using Ni/Pd/Au metallization
(2000-11-20)
Chu, CF
;
Yu, CC
;
Wang, YK
;
Tsai, JY
;
Lai, FI
In this letter, a low-resistance ohmic contact on p-type GaN using an alloy of Ni/Pd/Au is reported. The Mg doped p-type GaN samples were grown by metalorganic chemical vapor deposition with a carrier concentration of 4.1x10(17) cm(-3). The as-grown Mg doped samples were deposited with Ni (20 nm)/Pd (20 nm)/Au (100 nm) and then annealed in air, nitrogen, and oxygen ambient conditions at different annealing temperatures ranging from 350 to 650 degreesC. Linear I-V ohmic characteristics were observed with specific resistance as low as 1.0x10(-4) Omega cm(2) for the samples annealed in oxygen atmosphere. Similar contact metal composition was also deposited on Be-implanted p-type GaN samples with a carrier density of 8.1x10(19) cm(-3). Without further annealing process, the samples show good ohmic contact with a lowest specific resistance of 4.5x10(-6) Omega cm(2). (C) 2000 American Institute of Physics. [S0003-6951(00)01847-7].
Memory properties of metal/ferroelectric/semiconductor and metal/ferroelectric/insulator/semiconductor structures using rf sputtered ferroelectric Sr0.8Bi2.5Ta1.2Nb0.8O9 thin films
(2004-07-01)
Huang, CH
;
Wang, YK
;
Lue, HT
;
Huang, JY
;
Lee, MZ
Off-axis rf magnetron sputtering has been employed to grow Sr0.8Bi2.5Ta1.2Nb0.8O9 (SBTN) ferroelectric thin films with (115) preferred orientation on SiO2/Si and Si substrates. The lower temperature and the higher oxygen mixing ratios [OMR, O-2/ (Ar+O-2)] used in film processing lead to reduction in the leakage current densities and widening the memory window of the resultant metal-ferroelectric-insulator semiconductor (MRS) structures. The maximum memory windows of the MFIS structures based on 40% OMR SBTN films deposited at 500 degreesC on SiO2/Si substrate are 2.87 and 2.27 V at the bias amplitudes of 10 and 8 V, respectively. With increasing applied voltage, the memory window also increases. The memory window decreases from 2.27 to 1.59 V after the 10(11) switching cycles at a bias amplitude of 8 V. The capacitance difference, DeltaC, between the two states decreases by 48% after retention time of 7000 s. (C) 2003 Elsevier Ltd. All rights reserved.
Molecular cloning and functional characterization of hemolysin gene from Vibrio furnissii
(2005-07-01)
Wang, YK
;
Wu, TK
;
生物科技學系
;
Department of Biological Science and Technology
Pentacene-based thin film transistors used to drive a twist-nematic liquid crystal display
(2005-11-22)
Wang, YW
;
Cheng, HL
;
Wang, YK
;
Hu, TH
;
Ho, JC
The study addresses the factors of influence on the active matrix display that is driven by pentacene-based organic thin-film transistors (TFTs). The atmosphere and humidity conditions were found to seriously affect the performance of organic TFTs. An appropriate encapsulation layer was added to protect the organic TFTs from external damage. Organic TFTs reliability, the illumination effect and device uniformity, were also considered in the context of display application. Finally, a monochrome 3 inch 64 x 128 active-matrix twist-nematic liquid crystal display (LCD) was fabricated. The display is capable of showing video images with a refresh rate of 20 Hz. Obtained results reveal the potential of organic TFTs for active-matrix LCD technology. (c) 2005 Elsevier B.V All rights reserved.
Preferentially oriented ferroelectric Pb(Zr0.53Ti0.47)O(3)thin films on (110)BaRuO3/Ru/SiO2/Si substrates
(2004-01-01)
Wang, YK
;
Tseng, TY
;
Lin, P
;
材料科學與工程學系
;
電子工程學系及電子研究所
Ferroelectric Pb(Zr0.53Ti0.47)O-3 (PZT) thin films were deposited on BaRuO3 (BRO)/Ru/SiO2/Si substrates by a sol-gel method. The (110)-oriented BaRuO3 bottom electrode films were deposited by rf sputtering at various temperatures. Highly (110) preferentially oriented PZT films were formed after annealing at over 450degreesC. The leakage current, dielectric constant, loss tangent, and polarization vs. electric field properties were strongly dependent on the annealing temperature of the PZT films and the deposition temperature of BRO electrodes. The dielectric constant and polarization decreased when the annealing temperature of the PZT film was over 700degreesC, which may be due to the interdiffusion between PZT and BRO. (C) 2003 The Electrochemical Society.
Studies on ferroelectric properties of sol-gel derived Pb(Zr0.53Ti0.47)O-3 using Ba0.5Sr0.5RuO3 as the conductive electrodes
(2004)
Wang, YK
;
Huang, CH
;
Tseng, TY
;
Linb, P
;
材料科學與工程學系
Pb(Zr0.53Ti0.47)O-3 (PZT) thin films with a (110) preferred orientation were prepared on Ba0.5Sr0.5RuO3 (BSR)/Ru/SiO2/Si substrates using a sol-gel method. The oxide bottom electrode, BSR, was fabricated at various temperatures on Ru/SiO2/Si substrates by rf sputtering. The annealed PZT films on BSR/Ru/SiO2/Si substrates exhibited improved crystallinity. The electrical properties of PZT films, such as the electric field (E) induced variations of the leakage current density, the dielectric constant, and the polarization were strongly dependent on the processing temperatures of the PZT films as well as the bottom oxide electrode. A typical PZT thin film annealed at 650degreesC on the BSR electrode, which was deposited at 450degreesC on the Ru/SiO2/Si substrate by a sputtering technique, has a leakage current of 2.7 x 10(-7) A/cm(2) at an applied electric field of 500 kV/cm and a dielectric constant of 968. From the polarization-electric field characteristics, the remanent polarization and coercive field of the PZT were found to be 38.9 muC/cm(2) and 59.6 kV/cm, respectively, at an applied voltage of 5 V. The PZT films exhibited fatigue-free characteristics up to similar to1.0 x 10(12) switching cycles under 5 V bipolar pulses. (C) 2004 The Electrochemical Society.
Synthesis and characterization of thiazole-containing chromophores for second-order nonlinear optics
(1999-07-01)
Wang, YK
;
Shu, CF
;
Breitung, EM
;
McMahon, RJ
;
應用化學系
Push-pull thiazole-containing nonlinear optical chromophores with dicyanovinyl and tricyanovinyl accepters, along with their thiophene analogs, have been synthesized and characterized. The onset temperatures of thermal decomposition of these chromophores determined by DSC are:above;240 degrees C. The;redox properties of the chromophores were studied by cyclic voltammetry and the results reveal the electron-deficient (thiazole) and electron-excessive (thiophene) nature of the heterocycles. Experimental measurements of second-order nonlinear optical response (mu.beta) indicate that the combination of either,a thiazole or thiophene conjugating,unit and a tricyanovinyl acceptor results in a nonlinear optical chromephore exhibiting substantial molecular hyperpolarizability (mu.beta ca 7000 x 10(-48) cm(6) at 1907 nm).
Synthesis of nonlinear optical chromophores containing electron-excessive and -deficient heterocyclic bridges. The auxiliary donor-acceptor effects
(1998-04-01)
Shu, CF
;
Wang, YK
;
應用化學系
;
Department of Applied Chemistry
Push-pull substituted nonlinear optical chromophores with thiazole and thiophene rings and interposed ethylene units as pi-conjugated bridges were synthesized. The effects of the nature and location of the heterocycles on the energy of the charge transfer transition for the chromophores are discussed.