Browsing by Author "Lee, WI"

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A dopant-related defect in Te-doped AlInP
(1999-08-01)
Wu, YR
;
Sung, WJ
;
Wen, TC
;
Lee, SC
;
Lee, WI
A deep level in Te-doped Al0.5In0.5P, grown by metal organic chemical vapor deposition, has been studied by deep level transient spectroscopy. The thermal activation energy was 0.24 eV, and the trap concentration was related to Te-dopant concentration. The deep level concentration strongly increased with elevating Te-dopant concentration. Meanwhile, the trap distribution profile also presented the same distribution behavior as the Te concentration profile. Therefore, the deep level in Te-doped AlInP is verified to be a dopant-related defect.
Activation of p-type GaN in a pure oxygen ambient
(2001-05-15)
Wen, TC
;
Lee, SC
;
Lee, WI
;
Chen, TY
;
Chan, SH
In this study, we activated p-type GaN in a pure oxygen ambient by rapid thermal annealing. The sheet resistance of p-type GaN was greatly reduced from > 10(7) Omega/square to 7.06 x 10(4) Omega/square after annealing in oxygen ambient at 500 degreesC, The photoluminescence intensity of blue emission increased by one order of magnitude compared to the as-grown sample. Moreover, the sheet resistance of p-type GaN annealed in pure oxygen ambient is lower than that of p-type GaN annealed in nitrogen ambient. The carrier concentrations of the samples annealed in oxygen ambient are higher than those annealed in nitrogen ambient. The better activation of p-type GaN in oxygen ambient is due to the higher activity of oxygen than that of nitrogen. Oxygen would remove hydrogen that passivates Ma atoms by forming H2O at a lower temperature.
Analysis of influence of alkyl sources on deep levels in GaN by transient capacitance method
(1996-07-01)
Chen, JF
;
Chen, NC
;
Huang, WY
;
Lee, WI
;
Feng, MS
The transient capacitance method nas used to analyze GaN samples grown by low-pressure organometallic vapor phase epitaxy (OMVPE) with triethylgallium (TEGa) or trimethylgallium (TMGa) as the alkyl source. Two deep levels at 1.10 and 1.27 eV were observed in the TMGa sample, while a deep level at 0.60 eV was observed in the TEGa sample. Using light illumination, levels deeper than those above were investigated in TEGa and TMGa samples.
Analysis of influence of alkyl sources on deep levels in GaN by transient capacitance method
(1996-07-01)
Chen, JF
;
Chen, NC
;
Huang, WY
;
Lee, WI
;
Feng, MS
The transient capacitance method nas used to analyze GaN samples grown by low-pressure organometallic vapor phase epitaxy (OMVPE) with triethylgallium (TEGa) or trimethylgallium (TMGa) as the alkyl source. Two deep levels at 1.10 and 1.27 eV were observed in the TMGa sample, while a deep level at 0.60 eV was observed in the TEGa sample. Using light illumination, levels deeper than those above were investigated in TEGa and TMGa samples.
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.
Characterization of p-type InxGa1-xN grown by metalorganic chemical vapor deposition
(2001-03-01)
Wen, TC
;
Lee, WI
;
Sheu, JK
;
Chi, GC
;
友訊交大聯合研發中心
This study investigates the electrical and optical characteristics of Mg-doped InxGa1-xN grown by metalorganic chemical vapor deposition. All the Mg-doped InxGa1-xN layers show p-type conduction after thermal annealing. Room temperature (RT) carrier concentration increases exponentially with an In mole fraction increase. The highest hole concentration of bull; Mg-doped InxGa1-xN is 1.65 x 10(19) cm(-3). Also, the RT photoluminescence (PL) spectra of Mg related emissions in InxGa1-xN are displayed. However, the PL peak intensity becomes weak after the post-annealing process on Mg-doped InxGa1-xN. This degradation might be created by the surface dissociation during the post-annealing process. (C) 2001 Elsevier Science Ltd. All rights reserved.
Deep level transient spectroscopy depth profile measurements of polycrystalline zinc oxide ceramic
(1996-09-15)
Lee, WI
;
Young, RL
;
Chen, WK
;
交大名義發表
;
友訊交大聯合研發中心
A method is proposed for performing deep level transient spectroscopy depth profile measurements of defects in polycrystalline ZnO. A multilayer-chip ZnO varistor structure is adopted to minimize the number of grains connected in series. It is verified that the distributions of some defects near the ZnO grain boundary are highly nonuniform. Valuable information has been obtained from the measured defect distribution profiles.
Deep level transient spectroscopy depth profile measurements of polycrystalline zinc oxide ceramic
(1996-09-15)
Lee, WI
;
Young, RL
;
Chen, WK
;
電子物理學系
;
Department of Electrophysics
A method is proposed for performing deep level transient spectroscopy depth profile measurements of defects in polycrystalline ZnO. A multilayer-chip ZnO varistor structure is adopted to minimize the number of grains connected in series. It is verified that the distributions of some defects near the ZnO grain boundary are highly nonuniform. Valuable information has been obtained from the measured defect distribution profiles.
Defects and degradation in ZnO varistor
(1996-07-22)
Lee, WI
;
Young, RL
;
交大名義發表
;
友訊交大聯合研發中心
;
National Chiao Tung University
A systematic study of the defects in ZnO has been performed. The two commonly observed levels (L1, L2), located at around 0.15 and 0.24 eV under the conduction band, have been identified as native defects. The deep level transient spectroscopy depth profiling technique is applied on multilayer-chip-type ZnO varistors to determine the distribution profiles of these two levels. With higher densities near the grain boundary, L2 is unlikely to be zinc interstitials as some previous studies have assigned, Both L1 and L2 show no apparent correlation with the device degradation process. Instead, a complex defect or interface trap, related to impurities in the starting material, exhibits a much stronger correlation with the ZnO varistor's stability. (C) 1996 American Institute of Physics.
Degradation phenomena of multilayer ZnO-glass varistors studied by deep level transient spectroscopy
(1996-09-16)
Wang, YP
;
Lee, WI
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The degradation of non-Ohmic electrical characteristics of ZnO-glass chip varistors due to high-intensity impulse currents was correlated with the deep trap levels investigated by means of deep level transient spectroscopy. Three electron traps located at 0.11, 0.27, and 0.94 eV below the conduction band were observed for chip varistors before current impulse testing. These trap energy depths of the chip varistors after current impulse testing were found to be almost unchanged, but their trap densities and capture cross sections both decreased. The concentration of the trap at 0.94 eV was decreased and ascribed to oxygen vacancies existing at the grain boundaries of the varistor. The electrical degradation phenomenon of the chip varistors is closely related to the reaction between the trap at 0.94 eV and adsorbed oxygen ions at the grain boundaries. (C) 1996 American Institute of Physics.
Degradation phenomena of multilayer ZnO-glass varistors studied by deep level transient spectroscopy
(1996-09-16)
Wang, YP
;
Lee, WI
;
Tseng, TY
;
電子物理學系
;
電子工程學系及電子研究所
The degradation of non-Ohmic electrical characteristics of ZnO-glass chip varistors due to high-intensity impulse currents was correlated with the deep trap levels investigated by means of deep level transient spectroscopy. Three electron traps located at 0.11, 0.27, and 0.94 eV below the conduction band were observed for chip varistors before current impulse testing. These trap energy depths of the chip varistors after current impulse testing were found to be almost unchanged, but their trap densities and capture cross sections both decreased. The concentration of the trap at 0.94 eV was decreased and ascribed to oxygen vacancies existing at the grain boundaries of the varistor. The electrical degradation phenomenon of the chip varistors is closely related to the reaction between the trap at 0.94 eV and adsorbed oxygen ions at the grain boundaries. (C) 1996 American Institute of Physics.
Electrooptical properties of GaNAs/GaAs multiple quantum well structures
(2003-07-25)
Lee, JR
;
Chen, YY
;
Lu, CR
;
Lee, WI
;
Lee, SC
The electrooptical properties of the GaNAs/GaAs multiple quantum well structures have been studied using the photoreflectance spectroscopy from 20 K to room temperature. Above the band gap energy of GaAs, Franz-Keldysh oscillations were observed. The period of the Franz-Keldysh oscillations decreased slightly with decreasing temperature, and indicated that the corresponding space charge distribution varied slowly with temperature. The modulated quantum well transition features were observed below the band gap energy of GaAs. A matrix transfer algorithm was used to calculate the quantum well subband energies numerically. The band gap energy and the electron effective mass of the GaNAs/GaAs system were adjusted to obtain the subband energies to best fit the observed quantum well transition energies. (C) 2003 Elsevier Science B.V. All rights reserved.
Formation of two-dimensional arsenic precipitation in superlattice structures of alternately undoped and heavily Be doped GaAs with varying periods grown by low-temperature molecular beam epitaxy
(1998-05-01)
Su, ZA
;
Huang, JH
;
Lee, WI
;
電子物理學系
;
Department of Electrophysics
As precipitates in superlattice structures of alternately undoped and [Be] = 2.4 x 10(20) cm(-3) doped GaAs with varying periods grown by molecular beam epitaxy at low substrate temperatures were studied by transmission electron microscopy. Never arsenic precipitate microstructures were observed in annealed samples, including preferential accumulation of precipitates inside the Be-doped GaAs but near each interface of Be-doped GaAs and the following grown undoped GaAs. The confinement reaches the extreme for samples annealed at 800 degrees C, where the precipitates appear as dot arrays along such interfaces and leave other areas almost free of precipitates. The incorporation of substitutional Be accepters is believed to cause a smaller lattice constant in the heavily Be-doped regions than in the undoped regions. A strain-induced mechanism was proposed to account for the preferential segregation of As clusters, though the underlying mechanism is not fully clear. (C) 1998 Elsevier Science B.V. All rights reserved.
Ga0.5In0.5P barrier layer for wet oxidation of AlAs
(2000-05-01)
Lee, SC
;
Lee, WI
;
電子物理學系
;
Department of Electrophysics
We study the stability of Ga0.5In0.5P acid Al0.4Ga0.6As barrier layers for wet thermal oxidation of AlAs on GaAs. Samples with a Ga0.5In0.5P or Al0.4Ga0.6As barrier layer are oxidized in a water vapor environment under various oxidation conditions. The results of photoluminescence and secondary-ion mass spectrometry (SIMS) depth profile measurements indicate that the Ga0.5In0.5P barrier layer is more stable than the Al0.4Ga0.6As layer at higher oxidation temperatures and longer periods of oxidation time.
Influence of barrier growth temperature on the properties of InGaN/GaN quantum Well
(2001-09-01)
Wen, TC
;
Lee, WI
;
電子物理學系
;
友訊交大聯合研發中心
;
Department of Electrophysics
In this study we investigate the effect of barrier growth temperature on the properties of InGaN/GaN multiple quantum wells. Double-crystal X-ray diffraction of MQW structures indicates that increasing the barrier growth temperature will reduce the well thickness. However, the photoluminescence peak wavelength shift is greater than the change of in the effective bandgap due to the reduction of well width. In addition to the reduction of well width, the determination of the origin of the significant blue shift in the photoluminescence peak wavelength should also take the strain effect into account.
Influence of barrier growth temperature on the properties of InGaN/GaN quantum wells
(2001)
Wen, TC
;
Lee, SC
;
Lee, WI
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
This study invests the effect of barrier growth temperature on the properties of InGaN/GaN MQW. Increase the growth temperature will reduce the well thickness and result in the blue shift of the PL peak. This blue shift in FL peak wavelength may be resulted from the stain occure during varying barrier growth temperature rather than only the reduce the well width. Moreover, we introduce a phase separation enhance layer into InGaN/GaN MQW. This layer join with the variation of barrier growth temperature will enhance the phase separation in InGaN/GaN MQW. There are two peaks clearly revealed in RT PL spectra. The higher energy peak might originate the InGaN quasi-wetting layer on the GaN barrier surface. The other one is interpreted of localize state at potential fluctuation owning to phase separation.
Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance
(2005-01-01)
Lee, JR
;
Lu, CR
;
Lee, WI
;
Lee, SC
;
電子物理學系
We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state. (C) 2004 Elsevier B.V. All rights reserved.
Liquid phase deposited SiO2 on GaN
(2003-04-29)
Wu, HR
;
Lee, KW
;
Nian, TB
;
Chou, DW
;
Wu, JJH
An efficient and low cost approach to deposit uniform silicon dioxide layers on GaN by liquid phase deposition (LPD) near room temperature are described and discussed. The process is simple. GaN wafers are immersed into a H2SiF6 and H3BO3 solution to form the silicon dioxide layers. The deposition conditions and the properties of the SiO2 films will be characterized. (C) 2002 Elsevier Science B.V. All rights reserved.
Low resistance Ohmic contacts to n-GaN by Ar plasma and forming gas ambient treatments
(2003-07-01)
Lee, CC
;
Lee, CP
;
Yeh, MH
;
Lee, WI
;
Kuo, CT
In this article, a scheme for fabricating low resistance Ohmic contacts to n-GaN was developed. This approach takes advantage of Ar plasma treatment and thermal annealing in forming gas ambient. As a result, the adjustment of Ar flow rate was very effective in improving the contact resistance. After proper Ar plasma treatment, the contact resistance and specific contact resistance of as-deposited Ohmic contacts were reduced to 0.362 Omega mm and 3.9 x 10(-5) Omega cm(2), respectively. Low contact resistance (0.103 Omega mm) and specific contact resistance (3.2 x 10(-6) Omega cm(2)) were obtained after annealing in N-2 gas ambient. By performing thermal annealing in forming gas ambient, even lower contact resistance (0.093 Omega mm) and specific contact resistance (2.6 x 10(-6) Omega cm(2)) were successfully achieved, indicating that the electrical characteristics of Ohmic contacts would not be affected by the effect of hydrogen passivation of dopants in n-GaN. (C) 2003 American Vacuum Society.
Majority- and minority-carrier traps in Te-doped AlInP
(1999-01-11)
Wu, YR
;
Sung, WJ
;
Lee, WI
;
電子物理學系
;
友訊交大聯合研發中心
The properties of deep levels found in Te-doped AlInP grown by metal-organic chemical vapor deposition have been studied. By using pn-junction structure, both minority- and majority-carrier traps can be observed. Two deep levels are found in Te-doped AlInP: one majority-carrier trap and one minority-carrier trap. The activation energies of majority- and minority-carrier traps are 0.24+/-0.05 and 0.25+/-0.03 eV, respectively. The majority-carrier trap is uniformly distributed, indicating that this level belongs to some kind of bulk defect. (C) 1999 American Institute of Physics. [S0003-6951(99)05202-X].