Browsing by Author "Tsai, Wen-Che"

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Direct near-field mapping of photoelectric response induced by localized surface plasmon of silver nano-islands on a silicon solar cell
(2012)
Yang, Cheng-Ying
;
Chen, Ting-Gang
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Chiang, Chien-Lang
;
Liou, Yi-Ying
;
Tsai, Wen-Che
We investigate the possibility to enhance the absorption in solar cells by employing localized plasmon polaritons excited in metallic nanostructure. one possible mechanism for increased absorption for the presence of the metallic nanostructure are the giant near-field enhancement. The localized near-field enhancement of electric field is near the surface of nanostructure within several ten nanometers. To observed the effect of localized surface Plasmon, the photoelectric conversion characteristics of a solar cell with metal nanostructure are investigated by using an illumination-collection mode scanning near-field optical microscopy and near-field optical beam induced current (NOBIC) technique.
Effects of growth temperature on InN/GaN nanodots grown by metal organic chemical vapor deposition
(2008-05-15)
Chang, Wen-Hao
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Ke, Wen-Cheng
;
Yu, Shu-Hung
;
Lee, Lin
;
Chen, Ching-Yu
InN nanodots grown on GaN by metal organic chemical vapor deposition using conventional growth mode as well as flow-rate modulation epitaxy at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN nanodots and their photoluminescence (PL) properties. The sample grown at around 650 degrees C showed the highest growth rate. For samples grown at higher temperatures, the residual carrier concentration was reduced and the PL efficiency was improved. Furthermore, we found that the growth of InN nanodots is still sustainable even at a temperature higher than 700 degrees C while retaining their optical quality. (c) 2008 American Institute of Physics.
Growth of sparse arrays of narrow GaN nanorods hosting spectrally stable InGaN quantum disks
(2012-07-16)
Chen, Yen-Ting
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Tsai, Wen-Che
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Chen, Wen-Yen
;
Hsiao, Ching-Lien
;
Hsu, Hsu-Cheng
Wafer-scale production of single InGaN quantum disks (QD) in-a-nanorod array with small rod diameter (> 9 nm) and low rod-density (< 10(8) cm(-2)) has been achieved without extensive processing steps. Excitation power-dependent mu PL spectrum of single QD reveals multi-excitonic peak with 0.75 meV blue-shift for 3 orders of magnitude increasing power, indicating the present system is spectrally stable and nearly free of quantum-confined Stark effects, due possibly to the strain relaxation induced by free surface of small rod diameters. The fully polarized emissions, a high working temperature (180 K), low rod density and good alignment, render this system promising as a potential quantum photon source. (C) 2012 Optical Society of America
Linear photon up-conversion of 450 meV in InGaN/GaN multiple quantum wells via Mn-doped GaN intermediate band photodetection
(2011-11-07)
Huang, Feng-Wen
;
Sheu, Jinn-Kong
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Lee, Ming-Lun
;
Tu, Shang-Ju
;
Lai, Wei-Chih
Up-converted heterostructures with a Mn-doped GaN intermediate band photodetection layer and an InGaN/GaN multiple quantum well (MQW) luminescence layer grown by metal-organic vapor-phase epitaxy are demonstrated. The up-converters exhibit a significant up-converted photoluminescence (UPL) signal. Power-dependent UPL and spectral responses indicate that the UPL emission is due to photo-carrier injection from the Mn-doped GaN layer into InGaN/GaN MQWs. Photons convert from 2.54 to 2.99 eV via a single-photon absorption process to exhibit a linear up-conversion photon energy of similar to 450 meV without applying bias voltage. Therefore, the up-conversion process could be interpreted within the uncomplicated energy level model. (C) 2011 Optical Society of America
Optical properties associated with strain relaxations in thick InGaN epitaxial films
(2014-03-10)
Tsai, Wen-Che
;
Hsu, Chia-He
;
Fu, Shao-Fu
;
Lee, Fang-Wei
;
Chen, Chin-Yu
Structural and optical properties of thick InGaN layers with strain and composition inhomogeneities are investigated. High resolution x-ray diffractions (XRD) and reciprocal space mapping (RSM) along an asymmetric axis reveal that the In composition inhomogeneity is accompanied by strain relaxations during the growth of thick InGaN layers. According to the structural analysis, the commonly observed double photoluminescence (PL) peaks have been confirmed to be associated with the strain relaxation in thick InGaN films. Temperature-dependent PL measurements further indicate that the relaxed phase in InGaN films exhibits better emission efficiency than the strained phase. Recombination dynamics reveal that the carrier localization effect is more pronounced in the relaxed phase due to the compositional pulling effect. The correlations between emission efficiency and localization effect in thick InGaN films are discussed. (C)2014 Optical Society of America
Optical properties of Mn in regrown GaN-based epitaxial layers
(2012-04-01)
Huang, Feng-Wen
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Sheu, Jinn-Kong
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Tu, Shang-Ju
;
Chen, Po-Cheng
;
Yeh, Yu-Hsiang
The memory effect and redistribution of manganese (Mn) into subsequently regrown GaN-based epitaxial layers by metalorganic chemical vapor deposition were revealed. Low-temperature up-converted photoluminescence (UPL) and the secondary ion mass spectrometry were performed on GaN-based epitaxial samples with and without Mn doping to study the effect of residual Mn on optical property. UPL emission, which originated from residual Mn doping in regrown InGaN quantum wells (QWs) because of the memory effect of the reactor, could be eliminated in an air-exposed and H-2-baking manner prior to the regrowth of the QWs. Considerable residual Mn background level and slow decay rate of Mn concentration tail were also observed in the regrown epitaxial layers, which could be attributed to the memory effect or surface segregation and diffusion from the Mn-doped underlying layer during regrowth in the Mn-free reactor. (C) 2012 Optical Society of America
Size-dependent strain relaxation in InN islands grown on GaN by metalorganic chemical vapor deposition
(2009-02-09)
Tsai, Wen-Che
;
Lin, Feng-Yi
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Ke, Wen-Cheng
;
Lu, Shu-Kai
;
Cheng, Shun-Jen
We report Raman measurements on InN islands grown on GaN by metalorganic chemical vapor deposition. The Raman frequency of the InN E(2) mode is found to decrease exponentially with the island's aspect ratio, indicating a size dependent strain relaxation during the island formation. Our results suggest that most of the strain at the InN-GaN interface have been released plastically during the initial stage of island formations. After that, the residual strain of only -3.5x10(-3) is further relaxed elastically via surface islanding. The experimental data are in agreement with the strain relaxation predicted from a simplified model analysis as well as three-dimensional finite-element simulations.
Structural and optical properties of In-rich InGaN nanodots grown by metallo-organic chemical vapor deposition
(2007-10-10)
Tsai, Wen-Che
;
Lin, Hsuan
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Ke, Wen-Chen
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Chang, Wen-Hao
;
Chou, Wu-Ching
The surface morphologies, alloy compositions and emission properties of In- rich InxGa1-xN nanodots ( x >= 0.87) grown by metallo-organic chemical vapor deposition at various growth temperatures (550-750 degrees C) were investigated. We found that the nucleation of InGaN dots was dominated by the surface migration of In adatoms. A higher Ga content can be achieved at lower growth temperatures due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the InGaN dots tend to decompose into In- rich islands and a thin Ga-rich layer. These In- rich islands exhibit photoluminescence emission in the near-infrared range. Another visible emission band was also observed for samples grown at higher temperatures. The formation of a thin Ga-rich layer is likely to be responsible for the visible emission.
Structural and optical properties of indium-rich InGaN islands
(2008)
Tsai, Wen-Che
;
Lin, Hsuan
;
Ke, Wen-Chen
;
Chang, Wen-Hao
;
Chou, Wu-Ching
Indium-rich InxGa1-xN islands (x >= 0.87) grown by metalor-ganic chemical vapor deposition at growth temperatures ranging from 550-750 degrees C were investigated. With the increasing growth temperature, the InGaN dot size increases while the dot density decreases due to the enhanced surface migration of In/Ga adatoms at elevated temperatures. In addition, the compositiom of InGaN-islands was also found to be varied with the growth temperature. At lower growth temperatures, a higher Ga content can be achieved due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the deposited InGaN material tend to decompose into In-rich islands and a thin Ga-rich layer, Photoluminescence investigations show that these In-rich islands exhibit a near-infrared emission band . For samples grown at higher temperatures a visible emission band was also observed. The visible emission band may arise from defect hands introduced during the formation of Ga-rich InGaN layer. (c) 2008 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.
Structural and optical properties of InN/GaN nanodots grown by metalorganic chemical vapor deposition
(2008)
Chang, Wen-Hao
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Lee, Lin
;
Chen, Ching-Yu
;
Tsai, Wen-Che
;
Lin, Hsuan
InN nanodots grown on GaN by metalorganic chemical vapor deposition (MOCVD) using conventional growth mode as well as flow-rate modulation epitaxy (FME) at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN dots and their photoluminescence (PL) properties. The best growth efficiency of InN was achieved by FME at around 650 degrees C. The residual carrier concentration and PL efficiency was also be improved when a high growth temperature was used. Our results indicated that InN nanodots can be grown at a temperature even higher than 700 degrees C while maintain their optical quality. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Suppressed piezoelectric polarization in single InGaN/GaN heterostructure nanowires
(2013-10-28)
Tsai, Wen-Che
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Chen, Yen-Ting
;
Lin, Chia-Hsien
;
Hsu, Wei-Ting
;
Hsu, Yung-Sheng
The optical properties of single InGaN/GaN heterostructure nanowires (NWs) with a mean diameter down to 18 nm are investigated. Sharp emission lines originating from the recombination of localized excitons in the InGaN disk layer can be resolved. Excitation-dependent energy shifts, together with spectral diffusions of these emission lines, indicate the presence of a weak quantum confined Stark effect (QCSE) caused by nearby charge fluctuations, rather than the screening of piezoelectric polarizations at the InGaN/GaN interface. The absence of a piezoelectric polarization field is further confirmed by time-resolved photoluminescence measurements. Numerical simulations reveal that the elastic strain relaxation via the NW geometry is marginal and occurs only near the NW sidewalls. Carrier localization preferentially near the periphery of the InGaN disk and alloy intermixing are suggested as possible reasons for the absence of a polarization-induced QCSE in thin InGaN/GaN heterostructure NWs.