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Now showing 1 - 8 of 8

Light Emission Characteristics of Nonpolar a-Plane GaN-Based Photonic Crystal Defect Cavities
(2016-09)
Kao, Tsung Sheng
;
Wu, Tzeng-Tsong
;
Tsao, Che-Wei
;
Lin, Jyun-Hao
;
Lin, Da-Wei
In this paper, the light emission performance from nonpolar a-plane gallium nitride (GaN)-based photonic crystal (PC) slabs with line-type defect cavities has been investigated. Via the focused ion beam milling technique, thin membrane structures of the nonpolar GaN PC defect cavities were engineered, exhibiting one dominated resonant mode occurred at 419.3 nm with a high quality factor of 1.9 x 10(3) in the photoluminescence emission characterizations. In the far-field region, light emission performance shows a high polarization degree of 50% with the beam direction perpendicular to the defect cavity. Compared with the PC defect cavity patterns fabricated on c-axial oriented GaN materials, the a-plane PC defect cavities display not only the linear light output-input power dependence, but also an invariant resonant mode of constant light emission behavior with increasing the injection carriers, therefore providing a new perspective for the future development of promising optoelectronic devices.
Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe2 by Hydrohalic Acid Treatment
(2016-01)
Han, Hau-Vei
;
Lu, Ang-Yu
;
Lu, Li-Syuan
;
Huang, Jing-Kai
;
Li, Henan
Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.
Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe2 by Hydrohalic Acid Treatment
(2016-01-01)
Han, Hau-Vei
;
Lu, Ang-Yu
;
Lu, Li-Syuan
;
Huang, Jing-Kai
;
Li, Henan
Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.
Thermally evaporated In2O3 nanoloquats with oxygen flow-dependent optical emissions
(2008-02-15)
Chu, Chia-Pu
;
Ko, Tsung-Shine
;
Chang, Yu-Cheng
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
We report the synthesis of the In2O3 nanoloquat grown at different oxygen flow rates by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth Of In2O3 nanoloquats. The nanostructures of the In2O3 nanoloquats were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photoluminescence (PL) study reveals that In2O3 nanoloquats could emit different luminescence peaks in the range of 500-600 nm with broad bands by adjusting different oxygen flow rates. The coverage of the wavelength tuning in the emission peaks of the In2O3 nanoloquats could be beneficial for possible applications in white light illumination through manipulating the ratio of each wavelength component. (c) 2007 Published by Elsevier B.V.
Tunable light emissions from thermally evaporated In2O3 nanostructures grown at different growth temperatures
(2008-04-01)
Ko, Tsung-Shine
;
Chu, Chia-Pu
;
Chen, Jun-Rong
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
We report the synthesis of the In2O3 nanostructures grown at different growth temperatures by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth of In2O3 nanostructures. The nanostructures of the In2O3 were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The photo luminescence study reveals that In2O3 nanostructures could emit different luminescence peaks in the range of 400-600 nm with broad bands by adjusting different growth temperatures. The coverage of the wavelength tuning in the emission peaks of the In2O3 nanostructures could be beneficial for possible applications in white light illumination through manipulating the ratio of each wavelength component. (C) 2007 Elsevier B.V. All rights reserved.
Characterization of large area Cu(In,Ga)Se-2 nanotip arrays via photoluminescence
(2012)
Liao, Yu-Kuang
;
Lin, Woei-Tyng
;
Hsieh, Dan-Hua
;
Kuo, Shou-Yi
;
Lai, Fang-I
In this study, photoluminescence (PL) measurements were used to characterized Cu(In,Ga)Se-2 nanotip arrays (CIGS NTRs). Large area CIGS NTRs were yielded by using one step Ar+ milling process without template. Formation mechanism of NTRs is due to a highly anisotropic milling effect of the quaternary components compound. In both CIGS thin films with and without NTRs, saturation effects of Donor-Acceptor Pair (DAP) had been observed while excitation power dependence PL measurements. Comparing with thin film CIGS without NTRs, it has revealed that the concentration DAP had been changed after formation of CIGS NTRs and had enhanced its carrier density of the p-type semiconductor.
Nanorod epitaxial lateral overgrowth of a-plane GaN with low dislocation density
(2009-06-22)
Ling, Shih-Chun
;
Chao, Chu-Li
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template. The investigation of x-ray diffraction showed that the strain in a-plane GaN grown on r-plane sapphire could be mitigated. The average threading dislocation density estimated by transmission electron microscopy was reduced from 3x10(10) to 3.5x10(8) cm(-2). From the temperature-dependent photoluminescence, the quantum efficiency of the a-plane GaN was enhanced by the nanorod epitaxial lateral overgrowth (NRELOG). These results demonstrated the opportunity of achieving a-plane GaN films with low dislocation density and high crystal quality via NRELOG.
Low Droop Nonpolar GaN/InGaN Light Emitting Diode Grown on m-Plane GaN Substrate
(2010)
Chang, Shih-Pang
;
Lu, Tien-Chang
;
Zhuo, Li-Fu
;
Jang, Chung-Ying
;
Lin, Da-Wei
The low droop nonpolar m-plane InGaN/GaN light emitting diode (LED) has been fabricated and investigated. The external quantum efficiency for a 300x300 mu m square LED chip only drops about 18% from maximum at an operation current of 22 A/cm(2) (20 mA) to 330 A/cm(2) (300 mA) dc operations at room temperature. In addition, the internal quantum efficiency has been extracted by temperature-dependent photoluminescence measurements, and there is no droop observed as the carrier density increases. The small droop in efficiency of m-plane LEDs could be due to the lack of polarization effects that enhances the carrier confinement under high current density operation. The polarization anisotropy is clearly observed in the m-plane LED, and the degree of polarization is 68%.

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