Browsing by Author "Lee, Y. C."

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AlGaInAs multiple-quantum-well 1.2-mu m semiconductor laser in-well pumped by an Yb-doped pulsed fiber amplifier
(2012-01-01)
Chen, Y. -F.
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Lee, Y. C.
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Huang, S. C.
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Huang, K. F.
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Chen, Y. F.
An AlGaInAs multiple quantum well structure is reported as an effective gain medium of the in-well pumped high-peak-power semiconductor disk laser at 1.2 mu m. We use an Yb-doped pulsed fiber amplifier as the pump source to effectively optimize the output characteristics. The maximum average output power of 1.28 W and peak output power of 0.76 kW is obtained at 1225 nm lasing wavelength under 60 kHz pump repetition rate and 28 ns pump pulse width.
Carrier dynamics in ZnxCd1-xO films grown by molecular beam epitaxy
(2016-01-01)
Cheng, F. J.
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Lee, Y. C.
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Hu, S. Y.
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Lin, Y. C.
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Tiong, K. K.
In this work, the carrier dynamics in Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system have been investigated using photoluminescence and time-resolved photoluminescence measurements. The carrier lifetime can be estimated from the PL decay curve fitted by triple exponential function. The emission energy dependence and temperature dependence of the PL decay time indicate that carrier localization dominate the luminescence mechanism of the ZnCdO alloy semiconductor.
Deformation of Multilayer Flexible Electronics Subjected to Torque
(2014-01-01)
Lee, Y. C.
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Liu, T. S.
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機械工程學系
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Department of Mechanical Engineering
Flexibility is one of remarkable characteristics of flexible electronics. Therefore, the analysis of flexible electronics deformation caused by external torques will help its design. In this work, analytical derivation is conducted for flexible electronics treated as multilayer structures. In experiments, an electric motor under computer control exerts a torque to generate torsion, whose twist angles are obtained by using both optical encoder measurement and theoretical calculation. Comparisons are made between experimental and theoretical results for bare PEN (polyethylene naphthalate) substrates of different sizes, multilayer PET (polyethylene terephthalate) substrates, and ITO (indium tin oxide)-coated PET substrates. Finally, a laser displacement sensor is used to measure the out-of-plane deformation for validating the proposed theoretical model.
Evaluating the Commercial Potential of Original Technologies in Universities
(2016-08)
Lee, Y. C.
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Lin, Grace T. R.
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Hsi, P. H.
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Lim, S. S.
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科技管理研究所
Since 2010, Ministry of Science and Technology (MOST) and Academia Sinica in Taiwan have formulated the Germination Program to translate important scientific discoveries into innovative developments. Using actual cases, this study aimed to propose a technology evaluation framework consisting of a hybrid fuzzy multi-criteria decision making (fuzzy MCDM) approach to evaluate and prioritize the optimal alternatives with best commercial potential. The fuzzy Delphi method was first used to determine the three dimensions and nine important decision criteria. Next, the fuzzy analytic hierarchy process (fuzzy AHP) results indicated that the top three dimensions are accordingly "technological innovation", "business development" and "operating management". The top three important criteria are "technological origins", "potential impact" and "technological competence" respectively. Finally, the fuzzy technique for order preference by similarity to ideal solution (fuzzy TOPSIS) results revealed that T2 and T4 are the two optimal alternatives with best commercial potential for further funding and commercialization. The proposed technology evaluation framework could serve as a reference to both government administrative agencies and university practitioners for the future evaluation of commercializing original technologies.
Exploring spatio-temporal dynamics of an optically pumped semiconductor laser with intracavity second harmonic generation
(2013)
Lee, Y. C.
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Liang, H. C.
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Tung, J. C.
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Su, K. W.
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Chen, Y. F.
We experimentally observe an intriguing phenomenon of complex spatio-temporal dynamics in a commercial optically pumped semiconductor laser with intracavity second harmonic generation. We numerically verify that the experimental results come from the total mode locking of TEM00 and higher-order modes with significant astigmatism. The scenarios of the spatio-temporal dynamics are quite similar to the phenomena in soft-aperture Kerr-lens mode locked Ti:sapphire lasers.
Femtosecond high-power spontaneous mode-locked operation in vertical-external cavity surface-emitting laser with gigahertz oscillation
(2011-12-01)
Chen, Y. F.
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Lee, Y. C.
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Liang, H. C.
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Lin, K. Y.
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Su, K. W.
We realize a femtosecond high-power spontaneous mode-locked operation with gigahertz oscillation in a vertical-external cavity surface-emitting laser under the condition of eliminating the internal and external unwanted reflection. We find that the reflectivity of the output coupler has a significant influence not only on the output power but also on the output pulse duration. With an incident pump power of 20W, we have achieved 2: 35W of average output power with 778 fs pulse duration at a repetition rate of 2: 17 GHz. The shortest pulse duration was 654 fs at an average output power of 0.45W. (C) 2011 Optical Society of America
High brightness GaN-based flip-chip light-emitting diodes by adopting geometric sapphire shaping structure
(2008-02-01)
Lee, C. E.
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Lee, Y. C.
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Kuo, H. C.
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Tsai, M. R.
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Lu, T. C.
GaN-based flip-chip LEDs (FC-LEDs) with geometric sapphire shaping structure were fabricated. The sapphire shaping structure was formed on the bottom side of the sapphire substrate by the chemical wet etching technique for the purpose of light extraction. The crystallography-etched facets were `(1 0 1 0) M-plane, (1 1 0 2) R-plane and (1 1 2 0) A-plane against the (0 0 0 1) c-axis with the angles range between similar to 29 degrees and similar to 60 degrees. It is demonstrated that the geometrical shape of the sapphire windows layer improves the light extraction efficiency. Compared to the conventional FC-LED, the sapphire-shaped FC-LED significantly enhanced the output power. The light output power of sapphire-shaped FC-LEDs was increased by 55% (at 350 mA current injection) compared to that of conventional FC-LEDs.
Improvement of luminescence from Si nanocrystals with thermal annealing in CO2
(2008-01-15)
Yang, M. D.
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Chu, A. H. M.
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Shen, J. L.
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Huang, Y. H.
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Yang, T. N.
Photoluminescence (PL) of Si nanocrystals with annealing in CO2 was studied using the continuous and time-resolved PL measurements. The PL intensity enhances as annealing temperature increases, which is attributed to passivation of the nonradiative recombination centers. As the annealing temperature is 950 degrees C the PL intensity has a maximum value, which increases about a factor of 3 than that of the untreated sample. Based on the emission energy dependence of the PL decay time, the depth of carrier localization is found to increase after the annealing in CO2. We suggest that the oxygen atoms desorbed from CO2 diffuse to react with Si nanocrystals and introduce localized states at the Si/SiO2 interface. (C) 2007 Elsevier B.V. All rights reserved.
Investigation on residual stress and stress-optical coefficient for flexible electronics by photoelasticity
(2012-04-01)
Lee, Y. C.
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Liu, T. S.
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Wu, C. I.
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Lin, W. Y.
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機械工程學系
For flexible electronics in manufacture, the full-field stress measurement is an important issue for the film deposited on the flexible substrate. In this work, the two-dimensional photoelasticity is proposed to measure stress-optical coefficients and an analytical derivation is carried out for investigation on full-field residual stresses under tensional forces. In experimental setup, a polarization beam splitter (PBS) is used to connect with two CCD cameras that are used to capture the intensity of right-hand and left-hand circular polarization separately. It has higher measured speed and better uniformity than a direct rotation method. Stress-optical coefficients can be calculated by extracting the slope from tensional stress versus optical retardation curve. Experimental results show that optical retardations for indium-tin-oxide (ITO)-coated PET (polyethylene terephthalate) substrates can be affected more easily than PET substrates under tensional forces. The difference of stress-optical coefficients between 0 degrees and 90 degrees orientations for PEN (polyethylene naphthalate) substrates is smaller than that for PET substrates. Furthermore, it shows residual stresses for ITO-coated PET substrates in 0 degrees and 90 degrees orientations are different under tensional stress. (C) 2011 Elsevier Ltd. All rights reserved.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07)
Das, Bipul
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Lee, Y. C.
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Li, L. C.
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Yi-Shiou, Liu
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Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge\'s relation, S-V (f) = AV(2)/f(alpha) (A is Hooge\'s like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07-01)
Das, Bipul
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Lee, Y. C.
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Li, L. C.
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Yi-Shiou, Liu
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Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge's relation, S-V (f) = AV(2)/f(alpha) (A is Hooge's like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Luminance enhancement of flip-chip light-emitting diodes by geometric sapphire shaping structure
(2008-01-01)
Lee, C. E.
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Kuo, H. C.
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Lee, Y. C.
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Tsai, M. R.
;
Lu, T. C.
The flip-chip light-emitting diodes (FC-LEDs) with geometric sapphire shaping structure were investigated. The sapphire shaping structure was formed on the. bottom side of the sapphire substrate by a chemical wet etching technique for light extraction purpose. The crystallography-etched facets were (1010) M-plane, (1102) R-plane, and (1120) A-plane against the (0001) c-axis with the angles range between 29 degrees similar to 60 degrees. These large slope oblique sidewalls are useful for light extraction efficiency enhancement. The light-output power of sapphire shaping FC-LEDs was increased 55% (at 350-mA current injection) compared to that of conventional FC-LEDs.
Magnetic tunnel junction based out-of-plane field sensor with perpendicular magnetic anisotropy in reference layer
(2015-05-07)
Lee, Y. C.
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Chao, C. T.
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Li, L. C.
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Suen, Y. W.
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Horng, Lance
A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co40Fe40B20 1.2 (reference)/MgO 2.0/Co20Fe60B20 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of similar to 27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of similar to 0.3%/Oe can achieve +/- 25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe. (C) 2015 AIP Publishing LLC.
Measuring junction temperature of GaAs solar cells using pulse-width modulation photoluminescence
(2010-07-01)
Yang, M. D.
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Liao, W. C.
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Shu, G. W.
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Liu, Y. K.
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Shen, J. L.
A photoluminescence (PL) technique is presented to measure the junction temperature of GaAs solar cells. The technique utilizes the pulse-width modulation of excitation laser and the temperature dependence of PL spectra. The apparent change of PL energy on duty cycle can be advantageously used for the determination of the junction temperature. Varying the duty cycle from 10% to 75% causes an increase of 2.9 Kin the junction temperature of GaAs solar cells. The carrier temperature of the junction layer was studied to confirm the result obtained from the pulse-width modulation PL (C) 2010 Elsevier Ltd. All rights reserved.
Observation of self-mode-locking assisted by high-order transverse modes in optically pumped semiconductor lasers
(2014-10-01)
Liang, H. C.
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Tsou, C. H.
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Lee, Y. C.
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Huang, K. F.
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Chen, Y. F.
The criterion for achieving the self-mode-locking (SML) in an optically pumped semiconductor laser (OPSL) with a linear cavity is systematically explored. Experimental results reveal that the occurrence of SML can be assisted by the existence of high-order transverse modes. Numerical analysis is performed to confirm that the critical pump power for obtaining the SML operation agrees very well with the pump threshold for exciting TEM1,0 mode. The present finding offers an important insight into laser physics and a useful indication for obtaining the SML operation in OPSLs.
On substrate behavior of flexible displays subjected to torque
(2011-08-01)
Lee, Y. C.
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Liu, T. S.
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Chang, Po-Yi
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Ku, Yi-Sha
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機械工程學系
In contrast to liquid-crystal displays (LCDs) and light-emitting-diode (LED) displays, flexible displays allow deformation. Therefore, it is worth studying the deformation of substrates in flexible displays. In this work, an analytical derivation is carried out for the torsion behavior of flexible substrates. Comparisons are made between deflection results of linear and non-linear elasticity analyses for substrates subject to four corner forces and torque, respectively. They show that when deflection becomes large, torques or forces needed for unit deformation also increase. Simulation results also show that when the substrate aspect ratio of length/width in display sizes increases, displays are easier to deform under torsion. In addition, polyethylene terephthalate (PET) substrates subject to torque are compared with polyethylene naphthalate (PFN) substrates. Finally, in experiments a fringe-reflection method and a four-step phase-shifting technique were carried out to validate the proposed non-linear model.
Orbital polarization of the unoccupied states in multiferroic LiCu(2)O(2)
(2008-12-01)
Chen, C. L.
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Yeh, K. W.
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Huang, D. J.
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Hsu, F. C.
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Lee, Y. C.
Using measurements of polarization-dependent soft-x-ray absorption and band-structure calculations including the on-site Coulomb interaction, we investigated the symmetry of the intrinsic 3d holes in the low-dimensional quantum magnet LiCu(2)O(2) with edge-sharing spin chains. The Cu L-edge and O K-edge measurements with in-plane and out-of-plane E vectors of x ray reveal the orbital character of the valence states of Cu on different sites. The unoccupied 3d states of nominal Cu(2+) exhibit predominantly xy symmetry, whereas 3d holes of 3z(2)-r(2) symmetry reside on the nominal Cu(+) sites. Both the experimental observations and theoretical calculations agree on the hybridization of the O 2p and Cu 3d states above the Fermi level. The existence of 3d holes on Cu(+) enhances the interlayer magnetic coupling.
Orbital polarization of the unoccupied states in multiferroic LiCu2O2
(2008-12-01)
Chen, C. L.
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Yeh, K. W.
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Huang, D. J.
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Hsu, F. C.
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Lee, Y. C.
Using measurements of polarization-dependent soft-x-ray absorption and band-structure calculations including the on-site Coulomb interaction, we investigated the symmetry of the intrinsic 3d holes in the low-dimensional quantum magnet LiCu2O2 with edge-sharing spin chains. The Cu L-edge and O K-edge measurements with in-plane and out-of-plane E vectors of x ray reveal the orbital character of the valence states of Cu on different sites. The unoccupied 3d states of nominal Cu2+ exhibit predominantly xy symmetry, whereas 3d holes of 3z(2)-r(2) symmetry reside on the nominal Cu+ sites. Both the experimental observations and theoretical calculations agree on the hybridization of the O 2p and Cu 3d states above the Fermi level. The existence of 3d holes on Cu+ enhances the interlayer magnetic coupling.
Output Power Enhancement of Vertical-Injection Ultraviolet Light-Emitting Diodes by GaN-Free and Surface Roughness Structures
(2009)
Lee, C. E.
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Cheng, B. S.
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Lee, Y. C.
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Kuo, H. C.
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Lu, T. C.
Nitride-based UV, vertical-injection light-emitting diodes (VLEDs) with GaN-free and surface roughness structures operating at 365 nm were proposed and demonstrated by a combination of wafer bonding and laser lift-off processes. The GaN-free structure offers a promising potential for enhancing the light output of UV-VLEDs. The 3.2x light output enhancement was performed by removing the GaN. With the help of adopting a roughened surface, the light-output power of the UV-VLEDs could be further enhanced by a factor of 2.3 as compared with that of UV-VLED without a roughened surface. The total enhancement of surface-roughened GaN-free UV-VLEDs was increased by a factor of 7.8 compared to that of conventional UV-LEDs at a driving current injection of 250 mA.
Photoluminescence of localized excitons in ZnCdO thin films grown by molecular beam epitaxy
(2016-07)
Wu, T. Y.
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Huang, Y. S.
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Hu, S. Y.
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Lee, Y. C.
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Tiong, K. K.
We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents. (C) 2016 Elsevier Ltd. All rights reserved.