Browsing by Author "Chen, Shih-Wei"

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13% Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell via Interface Engineering
(2013-12-01)
Yu, Peichen
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Tsai, Chia-Ying
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Chang, Jan-Kai
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Lai, Chih-Chung
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Chen, Po-Han
Interface carrier recombination currently hinders the performance of hybrid organic silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAP() layer into hybrid heterojunction solar cells based on silicon nanowires (SINWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAP( increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAP( can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.
AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique
(2008)
Lo, Ming-Hua
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Li, Zhen-Yu
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Chen, Shih-Wei
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Hong, Jhih-Cang
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Lu, Ting-Chang
We report the successful growth of high quality ultraviolet (UV) AlGaN/GaN multiple quantum wells (MQWs) structure using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW sample grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers comprised AlN/GaN superlattices (SLs). From atomic force microscope measurement, the root-mean-square value of the surface morphology was only 0.35 nm, and no crack was found on the surface. The dislocation density was estimated to be as low as 2x10(8) cm(-2). X-ray and transmission electron microscope data show the grown MQW has shape interface with good periodicity. The sample has a deep UV photoluminescence emission at 334 nm (3.71 eV) with a very narrow linewidth of 45 meV at 13K. The cathodoluminescence image show fairly uniform luminescence pattern at room temperature. In conclusion, the AlGaN/GaN MQW grown by ALD technique should be useful for providing high crystalline quality AlGaN/GaN-based MQW for fabrication of AlGaN/GaN-based UV light emitting devices such as light emitting diodes and lasers.
Angular-resolved Lasing Characteristics at Different Band Edges in GaN Photonic Crystal Surface Emitting Lasers
(2010)
Chen, Shih-Wei
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Lu, Tien-Chang
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Hou, Yun-Ju
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Liu, Ting-Chun
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Kuo, Hao-Chung
We successfully demonstrated and analyzed the angular-resolved characteristics of GaN-based photonic-crystal surface emitting lasers at different band edges (Gamma, K, and M), showing specific lasing angles in measured dispersion diagram. (C) 2010 Optical Society of America
Characteristics of Current-Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers
(2011-11-01)
Lu, Tien-Chang
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Wu, Tzeng-Tsong
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Chen, Shih-Wei
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Tu, Po-Min
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Li, Zhen-Yu
This paper reviews the fabrication technology and performance characteristics of current-injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with hybrid distributed Bragg reflectors (DBRs). The GaN-based VCSEL consists of a ten-pair Ta(2)O(5)/SiO(2) top DBR, a 7 lambda-thick optical cavity embedded with 10 InGaN/GaN multiquantum wells, and a 29-pair AlN/GaN bottom DBR. Lasing action is observed under continuous-wave operation at room temperature. The laser characteristics, such as temperature-dependent laser threshold current, emission wavelength, and spontaneous emission coupling factors, have been measured and discussed.
Characteristics of GaN-based photonic crystal surface emitting lasers
(2008-09-15)
Lu, Tien-chang
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Chen, Shih-Wei
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Kao, Tsung-Ting
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Liu, Tzu-Wei
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光電工程學系
Characteristics of GaN-based photonic crystal surface emitting lasers (PCSELs) were investigated and analyzed. The GaN-based PCSEL emits a blue wavelength at 401.8 nm with a linewidth of 1.6 angstrom and shows a threshold energy density about 2.7 mJ/cm(2) under the optical pumping at room temperature. The lasing wavelength emitted from PCSELs with different lattice constants occurs at the calculated band edges showing different polarization angles due to the light diffracted in specific directions, corresponding exactly to Gamma, K, and M directions in the K-space. Furthermore, the PCSEL also shows a spontaneous emission coupling efficiency beta of about 5 X 10(-3) and a characteristic temperature of 148 K. (C) 2008 American Institute of Physics.
Characteristics of GaN-based Vertical Cavity Surface Emitting Lasers with Hybrid Mirrors
(2011)
Lu, Tien-Chang
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Cheng, Bo Siao
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Wu, Tzeng-Tsong
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Chen, Shih-Wei
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Chen, Chien-Kang
We demonstrated CW current injection of GaN VCSELs with hybrid mirrors at room temperature. The laser characteristics, such as temperature dependent laser threshold current, spontaneous emission coupling factors, have been measured and discussed. (C)2011 Optical Society of America
Characteristics of large-scale nanohole arrays for thin-silicon photovoltaics
(2014-04-01)
Chen, Ting-Gang
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Yu, Peichen
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Chen, Shih-Wei
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Chang, Feng-Yu
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Huang, Bo-Yu
Nanostructured crystalline silicon is promising for thin-silicon photovoltaic devices because of reduced material usage and wafer quality constraint. This paper presents the optical and photovoltaic characteristics of silicon nanohole (SiNH) arrays fabricated using polystyrene nanosphere lithography and reactive-ion etching (RIE) techniques for large-area processes. A post-RIE damage removal etching is subsequently introduced to mitigate the surface recombination issues and also suppress the surface reflection due to modifications in the nanohole sidewall profile, resulting in a 19% increase in the power conversion efficiency. We show that the damage removal etching treatment can effectively recover the carrier lifetime and dark current-voltage characteristics of SiNH solar cells to resemble the planar counterpart without RIE damages. Furthermore, the reflectance spectra exhibit broadband and omnidirectional anti-reflective properties, where an AM1.5 G spectrum-weighted reflectance achieves 4.7% for SiNH arrays. Finally, a three-dimensional optical modeling has also been established to investigate the dimension and wafer thickness dependence of light absorption. We conclude that the SiNH arrays reveal great potential for efficient light harvesting in thin-silicon photovoltaics with a 95% material reduction compared to a typical cell thickness of 200 mu m. Copyright (c) 2012 John Wiley & Sons, Ltd.
Continuous wave operation of current injected GaN vertical cavity surface emitting lasers at room temperature
(2010-08-16)
Lu, Tien-Chang
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Chen, Shih-Wei
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Wu, Tzeng-Tsong
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Tu, Po-Min
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Chen, Chien-Kang
We report the demonstration of the continuous wave laser action on GaN-based vertical cavity surface emitting lasers at room temperature. The laser structure consists of a ten-pair Ta(2)O(5)/SiO(2) distributed Bragg reflector (DBR), a 7 lambda-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with an AlGaN electron blocking layer, and a 29-pair AlN/GaN DBR. The laser has a threshold current of about 9.7 mA corresponding to the current density of about 12.4 kA/cm(2) and a turn-on voltage about 4.3 V at 300 K. The lasing wavelength was 412 nm with a linewidth of about 0.5 nm. A spontaneous emission coupling efficiency factor of about 5x10(-3) and the degree of polarization of about 55% were measured, respectively. The laser beam has a narrow divergence angle of about 8 degrees. (C) 2010 American Institute of Physics. [doi:10.1063/1.3483133]
Crs
(2008)
Lu, Tien-Chang
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Kao, Tsung-Ting
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Chen, Shih-Wei
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Kao, Chih-Chiang
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Lin, Li-Fan
We report fabrication of GaN-based two-dimensional surface emitting photonic-crystal lasers and successful demonstration of lasing action at room temperature with the emission wavelength at 424.3 nm and a low threshold pumping energy density of 3.5 mJ/cm(2). (c) 2008 Optical Society of America
CW Lasing of Current Injection Blue GaN-Based Vertical Cavity Surface Emitting Lasers
(2008)
Lu, Tien-Chang
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Kno, Tsung-Ting
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Chen, Shih-Wei
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Kao, Chib-Chiang
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Kuo, Hao-Chung
We demonstrated CW laser operation of GAN-based VCSELs under current injection at 77K. CW laser action was achieved at a threshold current of 1.4mA, emitting at 462nm with a narrow linewidth of about 0.15nm. (c) 2008 Optical Society of America
Development of GaN-Based Vertical-Cavity Surface-Emitting Lasers
(2009-05-01)
Lu, Tien-Chang
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Chen, Jun-Rong
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Chen, Shih-Wei
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Kuo, Hao-Chung
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Kuo, Chien-Cheng
This paper reviews the fabrication technology and performance characteristics of optically pumped and electrically pumped GaN-based vertical-cavity surface-emitting lasers (VCSELs). The lasing action of optically pumped hybrid GaN-based VCSELs has been observed at room temperature due to the employment of high-quality and high-reflectivity AlN/GaN-based distributed Bragg reflectors in the VCSEL structure. Based on the device structure of the optically pumped hybrid GaN-based VCSELs, we further achieved the lasing action of electrically pumped GaN-based VCSELs under continuous-wave operation at 77 K. The laser has a threshold injection current of 1.4 mA and emits a blue wavelength at 462 nm together with a narrow linewidth of about 0.15 nm. The laser beam has a divergence angle of about 11.7 degrees with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5 x 10(-2) was measured.
Development of Telemedicine and Telecare over wireless sensor network
(2008)
Hsu, Shuo-Jen
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Wul, Hsin-Hsien
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Chen, Shih-Wei
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Liu, Tsang-Chi
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Huang, Wen-Tzeng
Telemedicine & Telecare aided by wireless sensor network (WSN) has recently become a health-caring trend in the future. However, the low data rate of WSN limited the acceptable quality of service. Researches [1-6] adopted ZigBee-based WSN to implement a platform and/or a telecare system. However, the capacity problem due to low data rate characteristic has not been addressed. Our research proposed an arrhythmia-aware telecare system and a new DSP-based WSN platform, enabling good digital signal processing performance! in ZigBee-based WSN. Proved by simulations and several real tests, combination of the proposed platform and system can provide a more bandwidth-conserving and reliable telecare system, with lower wireless traffic jam and higher stability.
GaN-based two-dimensional surface-emitting photonic crystal lasers with AlN/GaN distributed Bragg reflector
(2008-01-07)
Lu, Tien-Chang
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Chen, Shih-Wei
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Lin, Li-Fan
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Kao, Tsung-Ting
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Kao, Chih-Chiang
GaN-based two-dimensional (2D) surface-emitting photonic crystal (PC) lasers with AlN/GaN distributed Bragg reflectors are fabricated and demonstrated. The lasing threshold energy density is about 3.5 mJ/cm(2) per pulse under optical pumping at room temperature. Only one dominant emission wavelength of 424.3 nm with a narrow linewidth of 1.1 A above the threshold is observed. The laser emission covers whole circularly 2D PC patterns (50 mu m in diameter) with a small divergence angle. The lasing wavelength emitted from 2D PC lasers with different lattice constants occurs at the calculated band-edges provided by the PC patterns. The characteristics of large area, small divergence angle, and single mode emission from the GaN-based 2D surface-emitting PC lasers should be promising in high power blue-violet emitter applications.
High quality ultraviolet AlGaN/GaN multiple quantum wells with atomic layer deposition grown AlGaN barriers
(2008-09-29)
Li, Zhen-Yu
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Lo, Ming-Hua
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Hung, C. T.
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Chen, Shih-Wei
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Lu, Tien-Chang
Low dislocation density ultraviolet (UV) AlGaN/GaN multiple quantum well (MQW) structure was grown using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers formed by ALD grown AlN/GaN superlattices. The as-grown sample showed smooth surface morphology with a root-mean-square roughness value of only 0.35 nm, and no surface cracks were found. The dislocation density was estimated to be as low as 3.5 x 10(7) cm(-2). X-ray and transmission electron microscope data showed the MQW had sharp interfaces with good periodicity. The sample had an UV photoluminescence emission at 334 nm (3.71 eV) with a very narrow linewidth of 47 meV at 13 K. The cathodoluminescence image revealed a fairly uniform luminescence pattern at room temperature. The AlGaN/GaN MQW grown by ALD technique should be useful for providing high crystalline quality for fabrication of various optical devices. c 2008 American Institute of Physics.
HIT Solar Cell Performance Enhancement with Luminescent Down Shifting Phenomenon
(2018-01-01)
Lin, Albert
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Huang, Chien-Yao
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Parashar, Parag
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Chou, Hao-Ming
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Lin, Yi-Shiuan
Luminescent down-shifting (LDS) phenomenon has been employed to enhance the HIT solar cell efficiency. The efficiency and J(SC) are increased by 2.3% and 11.5% respectively. External quantum efficiency (EQE) data supports our claim.
Lasing Behavior, Gain Property, and Strong Coupling Effects in GaN-Based Vertical-Cavity Surface-Emitting Lasers
(2008-08-01)
Lu, Tien-Chang
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Chu, Jung-Tang
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Chen, Shih-Wei
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Cheng, Bo-Siao
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Kuo, Hao-Chung
The optical properties of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with two dielectric distributed Bragg reflectors were investigated under optically pumped operation. The laser emits blue-violet light at a wavelength of 414 nm at room temperature with a high spontaneous emission coupling factor (beta-factor) of 2 x 10(-2) and a linewidth of 0.25 nm. The optical gain was determined by the Hakki-Paoli method by measuring the photoluminescence spectra below threshold conditions. At room temperature, an optical gain of 2900 cm(-1) was obtained under threshold condition. The linewidth enhancement factor (alpha-factor) is estimated front the ratio of the wavelength and gain derivation with respect to the carrier density, and the alpha-factor at room temperature is estimated to be 2.8. Strong exciton-photon coupling in the microcavity was observed at room temperature. A 9 meV Rabi splitting with 60% peak-to-valley contrast was determined from the photoluminescence measurements. Emission spectra showing the evolution of anticrossing behavior were also observed.
Lasing Characteristics of GaN-based Photonic Crystal Surface-Emitting Lasers
(2009)
Chen, Shih-Wei
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Kao, Tsung-Ting
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Liu, Tzu-Wei
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Lu, Tien-Chang
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Kuo, Hao-Chung
We successfully demonstrated and analyzed the characteristics of GaN-based photonic-crystal surface emitting lasers at room temperature at different band edges (Gamma, K, and M), showing specific thresholds and polarization angles
Location-controlled-grain Technique for Monolithic 3D BEOL FinFET Circuits
(2018-01-01)
Yang, Chih-Chao
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Hsieh, Tung-Ying
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Huang, Po-Tsang
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Chen, Kuan-Neng
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Wu, Wan-Chi
A location-controlled-grain technique is presented for fabricating BEOL monolithic 3D FinFET ICs over SiO2. The grain-boundary free Si FinFETs thus fabricated exhibit steep sub-threshold swing (<70mV/doc.), high driving currents (n-type: 363 mu A/mu m and p-type: 385 mu A/mu m), and high I-on/I-off(>10(6)). According to simulation, the thickness of the interlayer dielectric plays an important role and shall be thicker than 250nm so that the sequential pulse laser crystallization process does not heat the bottom devices and interconnects to more than 400 degrees C.
Optically pumped GaN-based vertical cavity surface emitting lasers: Technology and characteristics
(2007-08-01)
Wang, Shing-Chung
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Lu, Tien-Chang
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Kao, Chih-Chiang
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Chu, Jong-Tang
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Huang, Gen-Sheng
We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AIN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed bv Ta2O5/SiO and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240K was measured, and a distinct spatially inhomooeneous emission pattern was observed.
Quantification and recognition of parkinsonian gait from monocular video imaging using kernel-based principal component analysis
(2011-11-10)
Chen, Shih-Wei
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Lin, Sheng-Huang
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Liao, Lun-De
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Lai, Hsin-Yi
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Pei, Yu-Cheng
Background: The computer-aided identification of specific gait patterns is an important issue in the assessment of Parkinson's disease (PD). In this study, a computer vision-based gait analysis approach is developed to assist the clinical assessments of PD with kernel-based principal component analysis (KPCA). Method: Twelve PD patients and twelve healthy adults with no neurological history or motor disorders within the past six months were recruited and separated according to their "Non-PD", "Drug-On", and "Drug-Off" states. The participants were asked to wear light-colored clothing and perform three walking trials through a corridor decorated with a navy curtain at their natural pace. The participants' gait performance during the steady-state walking period was captured by a digital camera for gait analysis. The collected walking image frames were then transformed into binary silhouettes for noise reduction and compression. Using the developed KPCA-based method, the features within the binary silhouettes can be extracted to quantitatively determine the gait cycle time, stride length, walking velocity, and cadence. Results and Discussion: The KPCA-based method uses a feature-extraction approach, which was verified to be more effective than traditional image area and principal component analysis (PCA) approaches in classifying "Non-PD" controls and "Drug-Off/On" PD patients. Encouragingly, this method has a high accuracy rate, 80.51%, for recognizing different gaits. Quantitative gait parameters are obtained, and the power spectrums of the patients' gaits are analyzed. We show that that the slow and irregular actions of PD patients during walking tend to transfer some of the power from the main lobe frequency to a lower frequency band. Our results indicate the feasibility of using gait performance to evaluate the motor function of patients with PD. Conclusion: This KPCA-based method requires only a digital camera and a decorated corridor setup. The ease of use and installation of the current method provides clinicians and researchers a low cost solution to monitor the progression of and the treatment to PD. In summary, the proposed method provides an alternative to perform gait analysis for patients with PD.