We have investigated the properties of organic light emitting diodes （OLEDs） with a nanopillar patterning structure at organic-metal or organic-organic interfaces. The results demonstrate that the introduction of a ...We have investigated the properties of organic light emitting diodes （OLEDs） with a nanopillar patterning structure at organic-metal or organic-organic interfaces. The results demonstrate that the introduction of a nanopillar structure can improve the light extraction efficiency greatly. We also find that the number, height, and position of nanopillars all affect the light extraction of OLEDs. The maximum power efficiency of a device with an optimized nanopillar patterning mode can be improved to 2.47 times that of the reference device. This enhancement in light extraction originates from the improved injected carriers, the broadened charge recombination zone, and the intensified wave guiding effects.展开更多
Two foundational factors （escape cone and transmissivity） about light extraction of light emitting diodes （LEDs） are discussed. According to these factors, a new process to simulate the light extraction of LEDs ba...Two foundational factors （escape cone and transmissivity） about light extraction of light emitting diodes （LEDs） are discussed. According to these factors, a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided. The improved method is to deal with the reflection and refraction of light （beam of light） at the interface between two mediums approximately. In addition, light extraction of traditional LEDs is simulated by different processes with the same structure and parameters. The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure. This method saves much time and improves efficiency in the simulation of light extraction of LEDs.展开更多
The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar, nanorough of P-CaN surface, coreshell and nano-interlayer st...The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar, nanorough of P-CaN surface, coreshell and nano-interlayer structure. From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures, especially those with an InGaN or AlCaN nano-interlayer. With a 420-nm luminescence wavelength, the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.展开更多
By simulating with finite-difference time-domain(FDTD) method, it is proved that two kinds of new photonic crystal slab(PCS) structures could enhance the light extraction efficiency of OLED. By comparing the results, ...By simulating with finite-difference time-domain(FDTD) method, it is proved that two kinds of new photonic crystal slab(PCS) structures could enhance the light extraction efficiency of OLED. By comparing the results, the most effective PCS structure with maximum light extraction efficiency(E_ r =1.99) is got. The optimized geometric parameters and optimized performance parameters of the PCS structures are also obtained.展开更多
The light extraction efficiency caused by total internal reflection is low. Based on the analysis of the existing technology, a new design scheme is proposed in this paper to improve the light extraction efficiency. T...The light extraction efficiency caused by total internal reflection is low. Based on the analysis of the existing technology, a new design scheme is proposed in this paper to improve the light extraction efficiency. The air gap photonic crystal is embedded on the GaN-based patterned sapphire substrate, which can reduce line misalignment and improve light extraction efficiency. The internal structure of the GaN-based LED epitaxial layer is composed of an electron emission layer, a quantum well in the light-emitting recombination region, and an electron blocking layer. Experimental results show that this method significantly improves the extraction efficiency of LED light.展开更多
AlGaN-based deep-ultraviolet(DUV)light-emitting diodes(LEDs)still face challenges in achieving high-quality AlGaN material and extracting the strong transverse magnetic(TM)mode emission(which is influenced by valence ...AlGaN-based deep-ultraviolet(DUV)light-emitting diodes(LEDs)still face challenges in achieving high-quality AlGaN material and extracting the strong transverse magnetic(TM)mode emission(which is influenced by valence band splitting inversion).Particularly,these challenges impact devices with wavelengths shorter than 250 nm on their optical power and wall-plug efficiency(WPE)due to an increased proportion of TM mode.Here,the plasmonic omni-directional reflective pad arrays were designed and introduced into the p-contact layer to enhance the light extraction for sub-250 nm DUV LEDs.Meanwhile,a novel device structure,to our knowledge,was put forward,integrating uniformly distributed n-type contact rods as an efficient light guide channel.The theoretical simulation demonstrated a light extraction improvement since these embedded plasmonic reflective pad arrays effectively altered the wavevector of transverse electric(TE)and TM mode photons from the quantum wells.An average enhancement of 12.5%in optical output power was attained in 249.5 nm DUV LEDs through the usage of the optimized diameter of the plasmonic pads.Furthermore,a quartz lens bonded with fluorine resin was introduced to improve refractive index matching at the light output interface,and a high optical power of 3.45 mW was achieved from the original 2.55 mW at a driven current of 100 mA.展开更多
We report a new method for the fabrication of two-dimensional photonic crystal （PhC） hole arrays to improve the light extraction of GaN-based light-emitting diodes （LEDs）. The PhC structures were realized using na...We report a new method for the fabrication of two-dimensional photonic crystal （PhC） hole arrays to improve the light extraction of GaN-based light-emitting diodes （LEDs）. The PhC structures were realized using nanospherical-lens photolithography and the selective-area epitaxy method, which ensured the electrical properties of the LEDs through leaving the p-GaN damage-free. At a current of 350 mA, the light output power of LEDs with PhC hole arrays of 450 nm and 600 nm in diameter with the same lattice period of 900 nm were enhanced by 49.3% and 72.2%, respectively, compared to LEDs without a PhC. Furthermore, the LEDs with PhC hole structures showed an obviously smaller divergent angle compared with conventional LEDs, which is consistent with the results of finite-difference time-domain simulation.展开更多
A nanowire （NW） structure provides an alternative scheme for deep ultraviolet light emitting diodes （DUV-LEDs） that promises high material quality and better light extraction efficiency （LEE）. In this report, we...A nanowire （NW） structure provides an alternative scheme for deep ultraviolet light emitting diodes （DUV-LEDs） that promises high material quality and better light extraction efficiency （LEE）. In this report, we investigate the influence of the tapering angle of closely packed AIGaN NWs, which is found to exist naturally in molecular beam epitaxy （MBE） grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic （TM） and transverse elec- tric （TE） polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.展开更多
Light extraction efficiency of organic light emitting diode （OLED） based on various photonic crystal slab （PCS） structures was studied. By using the finite-difference time-domain （FDTD） method, we investigated t...Light extraction efficiency of organic light emitting diode （OLED） based on various photonic crystal slab （PCS） structures was studied. By using the finite-difference time-domain （FDTD） method, we investigated the effect of several parameters, including filling factor and lattice constant, on the enhancement of light extraction efficiency of three basic PCSs, and got the most effective one. Two novel designs of ＂interlaced＂ and ＂double-interlaced＂ PCS structures based on the most effective basic PCS structure were introduced, and the ＂interlaced＂ one was proved to be even more efficient than its prototype. Large enhancement of light extraction efficiency resulted from the coupling to leaky modes in the expended light cone of a band structure, the diffraction in the space between columns, as well as the strong scattering at indium-tinoxide/glass interfaces.展开更多
The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extractio...The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.展开更多
H_5 photonic crystal（PC） microcavities co-implanted with erbium（Er） and oxygen（O） ions were fabricated on silicon-on-insulator（SOI） wafers.Photoluminescence（PL） measurements were taken at room temperature an...H_5 photonic crystal（PC） microcavities co-implanted with erbium（Er） and oxygen（O） ions were fabricated on silicon-on-insulator（SOI） wafers.Photoluminescence（PL） measurements were taken at room temperature and a light extraction enhancement of up to 12 was obtained at 1.54μm,as compared to an identically implanted unpatterned SOI wafer.In addition,we also explored the adjustment of cavity modes by changing the structural parameters of the PC,and the measured results showed that the cavity-resonant peaks shifted towards shorter wavelengths as the radius of the air holes increased,which is consistent with the theoretical simulation.展开更多
The internal quantum efficiency（IQE） of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency（EQE） and the light extraction efficiency（LEE）.The EQE can be measured experimen...The internal quantum efficiency（IQE） of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency（EQE） and the light extraction efficiency（LEE）.The EQE can be measured experimentally,but the LEE is difficult to calculate due to the complicated LED structures.In this work,a model was established to calculate the LEE by combining the transfer matrix formalism and an in-plane ray tracing method.With the calculated LEE,the IQE was determined and made a good agreement with that obtained by the ABC model and temperature-dependent photoluminescence method.The proposed method makes the determination of the IQE more practical and conventional.展开更多
At present, the use of rare earth elements（REEs） has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to co...At present, the use of rare earth elements（REEs） has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to control high volumes of liquids with electrical load. With the aim of improving a separation technology that would be superior to the existing extraction systems, the extraction behaviors of La（Ⅲ）,Pr（Ⅲ）, and Nd（Ⅲ） from an HCI medium with Cyanex 272 in the presence of the complexing agent lactic acid（HLac） and auxiliary agents citric acid（H3 Cit）, acetic acid（HAc）, and Titriplex Ⅲ have been reported.The effect of pH and lactic acid concentration has been examined. The use of lactic acid as a complexing agent leading to a high extraction of REEs with Cyanex 272 at pH = 5 was compared with systems without lactic acid. The results show that the use of acetic acid along with lactic acid leads to an increase in the extraction percentage of LREEs. While use of citric acid and Titriplex Ⅲ reduces the extraction percentage of LREEs. Finally, the presence of Titriplex Ⅲ together with lactic acid could lead to an increase in the separation factor of Pr and Nd.展开更多
Understanding the photon number statistics of a quantum emitter(QE)interacting with complex photonic environments is fundamental to advances in quantum optics and nanophotonics.We introduce a general theoretical frame...Understanding the photon number statistics of a quantum emitter(QE)interacting with complex photonic environments is fundamental to advances in quantum optics and nanophotonics.We introduce a general theoretical framework for calculating the modal photon number density spectrum(MPNDS)in arbitrary dielectric structures with an embedded two-level QE.We validate our approach by investigating a system composed of a two-level QE and a photonic crystal(PhC)slab with an L3 cavity and a waveguide,finding that the MPNDS exhibits significant changes in both waveguide and background radiative channels as the interaction between the QE and modal field transitions from weak coupling to strong coupling.We observe that the number of photons guided along the waveguide shows a strong dependence on the QE’s transition frequency and transition dipole moment,but demonstrates robustness to the transition dipole moment when the transition frequency approaches the waveguide cutoff frequency.Our work allows for the determination and tailoring of light emission characteristics across diverse radiative channels in complex photonic environments.展开更多
In this work,we design and fabricate a deep ultraviolet(DUV)light-emitting array consisting of 10×10 micro-LEDs(μ-LEDs)with each device having 20μm in diameter.Strikingly,the array demonstrates a significant en...In this work,we design and fabricate a deep ultraviolet(DUV)light-emitting array consisting of 10×10 micro-LEDs(μ-LEDs)with each device having 20μm in diameter.Strikingly,the array demonstrates a significant enhancement of total light output power by nearly 52%at the injection current of 100 mA,in comparison to a conventional large LED chip whose emitting area is the same as the array.A much higher(~22%)peak external quantum efficiency,as well as a smaller efficiency droop forμ-LED array,was also achieved.The numerical calculation reveals that the performance boost can be attributed to the higher light extraction efficiency at the edge of eachμ-LED.Additionally,the far-field pattern measurement shows that theμ-LED array possesses a better forward directionality of emission.These findings shed light on the enhancement of the DUV LEDs performance and provide new insights in controlling the light behavior of theμ-LEDs.展开更多
We report a feasible method to realize tun able surface plasm on-polarit on(SPP)res onance in orga nic light-emitt ing devices(OLEDs)by emplo ying corrugated Ag-Al alloy electrodes.The excited SPP res onance in duced ...We report a feasible method to realize tun able surface plasm on-polarit on(SPP)res onance in orga nic light-emitt ing devices(OLEDs)by emplo ying corrugated Ag-Al alloy electrodes.The excited SPP res onance in duced by the periodic corrugations can be precisely tuned based on the composition ratios of the Ag-Al alloy electrodes.With an appropriate composition ratio of the corrugated alloy electrode,the photons trapped in SPP modes are recovered and extracted effectively.The 25%in creaseme nt in luminance and 21%enhan ceme nt in curre nt efficie ncy have bee n achieved by using the corrugated Ag-Al alloy electrodes in OLEDs.展开更多
We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an...We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.展开更多
Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-...Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-based blue light LED,the model including deeply etched surface photonic crystals(PhCs)LED is discussed using mode analysis method from light waveguide theory.The distributions of all order modes in GaN layer are obtained by the effective index approximation.The light extraction efficiencies are also calculated by finite-difference time-domain method(FDTD).The emulated results fully coincide with the former analysis.Because the manufacture of the surface photonic crystal is feasible,the work can be very meaningful to design and manufacture the high efficiency GaN-based blue light LED in factory for a large amount.展开更多
With the rapid development of the machining and manufacturing industry,welding has been widely used in forming connections of structural parts.At present,manual methods are often used for welding and quality inspectio...With the rapid development of the machining and manufacturing industry,welding has been widely used in forming connections of structural parts.At present,manual methods are often used for welding and quality inspection,with low efficiency and unstable product quality.Due to the requirements of visual inspection of weld feature size,a visual inspection system for weld feature size based on line structured light(LSL)is designed and built in this paper.An adaptive light stripe sub-pixel center extraction algorithm and a feature point extraction algorithm for welding light stripe are proposed.The experiment results show that the detection error of the weld width is 0.216 mm,the detection error of the remaining height is 0.035 mm,the single measurement costs 109 ms,and the inspection stability and repeatability of the system is 1%.Our approach can meet the online detection requirements of practical applications.展开更多
240 nm AlGaN-based micro-LEDs with different sizes are designed and fabricated.Then,the external quantum efficiency(EQE)and light extraction efficiency(LEE)are systematically investigated by comparing size and edge ef...240 nm AlGaN-based micro-LEDs with different sizes are designed and fabricated.Then,the external quantum efficiency(EQE)and light extraction efficiency(LEE)are systematically investigated by comparing size and edge effects.Here,it is revealed that the peak optical output power increases by 81.83%with the size shrinking from 50.0 to 25.0μm.Thereinto,the LEE increases by 26.21%and the LEE enhancement mainly comes from the sidewall light extraction.Most notably,transversemagnetic(TM)mode light intensifies faster as the size shrinks due to the tilted mesa side-wall and Al reflector design.However,when it turns to 12.5μm sized micro-LEDs,the output power is lower than 25.0μm sized ones.The underlying mechanism is that even though protected by SiO2 passivation,the edge effect which leads to current leakage and Shockley-Read-Hall(SRH)recombination deteriorates rapidly with the size further shrinking.Moreover,the ratio of the p-contact area to mesa area is much lower,which deteriorates the p-type current spreading at the mesa edge.These findings show a role of thumb for the design of high efficiency micro-LEDs with wavelength below 250 nm,which will pave the way for wide applications of deep ultraviolet(DUV)micro-LEDs.展开更多
基金Project supported by the Program for Changjiang Scholar and Innovation Research Team in Universities of China(Grant No.IRT0972)the International Science&Technology Cooperation Program of China(Grant No.2012DFR50460)+1 种基金the National Natural Scientific Foundation of China(Grant Nos.21071108,60976018,21101111,61274056,and 61205179)the Key Innovative Research Team in Science and Technology of Shangxi Province,China(Grant No.2012041011)
文摘We have investigated the properties of organic light emitting diodes （OLEDs） with a nanopillar patterning structure at organic-metal or organic-organic interfaces. The results demonstrate that the introduction of a nanopillar structure can improve the light extraction efficiency greatly. We also find that the number, height, and position of nanopillars all affect the light extraction of OLEDs. The maximum power efficiency of a device with an optimized nanopillar patterning mode can be improved to 2.47 times that of the reference device. This enhancement in light extraction originates from the improved injected carriers, the broadened charge recombination zone, and the intensified wave guiding effects.
文摘Two foundational factors （escape cone and transmissivity） about light extraction of light emitting diodes （LEDs） are discussed. According to these factors, a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided. The improved method is to deal with the reflection and refraction of light （beam of light） at the interface between two mediums approximately. In addition, light extraction of traditional LEDs is simulated by different processes with the same structure and parameters. The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure. This method saves much time and improves efficiency in the simulation of light extraction of LEDs.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China (Grant No.60925017)the National Natural Science Foundation of China (Grant Nos.10990100 and 60836003)+2 种基金the National Basic Research Program of China (Grant No.2007CB936700)the National High Technology Research and Development Program of China (Grant No.2007AA03Z401)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.ISCAS2009T05O9S4050000)
文摘The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar, nanorough of P-CaN surface, coreshell and nano-interlayer structure. From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures, especially those with an InGaN or AlCaN nano-interlayer. With a 420-nm luminescence wavelength, the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.
文摘By simulating with finite-difference time-domain(FDTD) method, it is proved that two kinds of new photonic crystal slab(PCS) structures could enhance the light extraction efficiency of OLED. By comparing the results, the most effective PCS structure with maximum light extraction efficiency(E_ r =1.99) is got. The optimized geometric parameters and optimized performance parameters of the PCS structures are also obtained.
文摘The light extraction efficiency caused by total internal reflection is low. Based on the analysis of the existing technology, a new design scheme is proposed in this paper to improve the light extraction efficiency. The air gap photonic crystal is embedded on the GaN-based patterned sapphire substrate, which can reduce line misalignment and improve light extraction efficiency. The internal structure of the GaN-based LED epitaxial layer is composed of an electron emission layer, a quantum well in the light-emitting recombination region, and an electron blocking layer. Experimental results show that this method significantly improves the extraction efficiency of LED light.
基金National Key Research and Development Program of China(2022YFB3605103)National Natural Science Foundation of China(62234001)+1 种基金Key Scientific and Technological Program of Xiamen(3502Z20231016)Fundamental Research Funds for the Central Universities(20720240067)。
文摘AlGaN-based deep-ultraviolet(DUV)light-emitting diodes(LEDs)still face challenges in achieving high-quality AlGaN material and extracting the strong transverse magnetic(TM)mode emission(which is influenced by valence band splitting inversion).Particularly,these challenges impact devices with wavelengths shorter than 250 nm on their optical power and wall-plug efficiency(WPE)due to an increased proportion of TM mode.Here,the plasmonic omni-directional reflective pad arrays were designed and introduced into the p-contact layer to enhance the light extraction for sub-250 nm DUV LEDs.Meanwhile,a novel device structure,to our knowledge,was put forward,integrating uniformly distributed n-type contact rods as an efficient light guide channel.The theoretical simulation demonstrated a light extraction improvement since these embedded plasmonic reflective pad arrays effectively altered the wavevector of transverse electric(TE)and TM mode photons from the quantum wells.An average enhancement of 12.5%in optical output power was attained in 249.5 nm DUV LEDs through the usage of the optimized diameter of the plasmonic pads.Furthermore,a quartz lens bonded with fluorine resin was introduced to improve refractive index matching at the light output interface,and a high optical power of 3.45 mW was achieved from the original 2.55 mW at a driven current of 100 mA.
基金supported by the National Natural Science Foundation of China(No.61274040)the National Basic Research Program of China(No.2011CB301902)the National High Technology R&D Program of China(Nos.2011AA03A105,2011AA03A103)
文摘We report a new method for the fabrication of two-dimensional photonic crystal （PhC） hole arrays to improve the light extraction of GaN-based light-emitting diodes （LEDs）. The PhC structures were realized using nanospherical-lens photolithography and the selective-area epitaxy method, which ensured the electrical properties of the LEDs through leaving the p-GaN damage-free. At a current of 350 mA, the light output power of LEDs with PhC hole arrays of 450 nm and 600 nm in diameter with the same lattice period of 900 nm were enhanced by 49.3% and 72.2%, respectively, compared to LEDs without a PhC. Furthermore, the LEDs with PhC hole structures showed an obviously smaller divergent angle compared with conventional LEDs, which is consistent with the results of finite-difference time-domain simulation.
基金King Abdullah University of Science and Technology(KAUST)(KAUST Baseline Fund BAS/1/1614-01-01,KAUST Baseline Fund BAS/1/1664-01-01,KAUST Equipment Fund BAS/1/1664-01-07)National Natural Science Foundation of China(NSFC)(61774065)
文摘A nanowire （NW） structure provides an alternative scheme for deep ultraviolet light emitting diodes （DUV-LEDs） that promises high material quality and better light extraction efficiency （LEE）. In this report, we investigate the influence of the tapering angle of closely packed AIGaN NWs, which is found to exist naturally in molecular beam epitaxy （MBE） grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic （TM） and transverse elec- tric （TE） polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.
基金This work was supported by the 2005 Nano-Science and Technology Foundation of Science and Technology Committee of Shanghai Municipality under Grant No. 0452nm056.
文摘Light extraction efficiency of organic light emitting diode （OLED） based on various photonic crystal slab （PCS） structures was studied. By using the finite-difference time-domain （FDTD） method, we investigated the effect of several parameters, including filling factor and lattice constant, on the enhancement of light extraction efficiency of three basic PCSs, and got the most effective one. Two novel designs of ＂interlaced＂ and ＂double-interlaced＂ PCS structures based on the most effective basic PCS structure were introduced, and the ＂interlaced＂ one was proved to be even more efficient than its prototype. Large enhancement of light extraction efficiency resulted from the coupling to leaky modes in the expended light cone of a band structure, the diffraction in the space between columns, as well as the strong scattering at indium-tinoxide/glass interfaces.
基金the U.S. Department of Energy (Grant No. NE TL, DE-PS26-08NT00290)in part by the National Science Foundation (ECCS-1408051, CBET1120399)
文摘The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.
基金Project supported by the National Key Basic Research Special Fund of China(No.2007CB613404)the National High Technology Research and Development Program of China(No.2011AA010303)the National Natural Science Foundation of China(Nos.61090390, 60837001,60977045,60877014,60776057)
文摘H_5 photonic crystal（PC） microcavities co-implanted with erbium（Er） and oxygen（O） ions were fabricated on silicon-on-insulator（SOI） wafers.Photoluminescence（PL） measurements were taken at room temperature and a light extraction enhancement of up to 12 was obtained at 1.54μm,as compared to an identically implanted unpatterned SOI wafer.In addition,we also explored the adjustment of cavity modes by changing the structural parameters of the PC,and the measured results showed that the cavity-resonant peaks shifted towards shorter wavelengths as the radius of the air holes increased,which is consistent with the theoretical simulation.
基金supported by the National Natural Science Foundation of China(Nos.11574306,61334009)the China International Science and Technology Cooperation Program(No.2014DFG62280)the National High Technology Program of China(No.2015AA03A101)
文摘The internal quantum efficiency（IQE） of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency（EQE） and the light extraction efficiency（LEE）.The EQE can be measured experimentally,but the LEE is difficult to calculate due to the complicated LED structures.In this work,a model was established to calculate the LEE by combining the transfer matrix formalism and an in-plane ray tracing method.With the calculated LEE,the IQE was determined and made a good agreement with that obtained by the ABC model and temperature-dependent photoluminescence method.The proposed method makes the determination of the IQE more practical and conventional.
基金Project supported by Anguran Lead and Zinc Company(55/G/93)
文摘At present, the use of rare earth elements（REEs） has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to control high volumes of liquids with electrical load. With the aim of improving a separation technology that would be superior to the existing extraction systems, the extraction behaviors of La（Ⅲ）,Pr（Ⅲ）, and Nd（Ⅲ） from an HCI medium with Cyanex 272 in the presence of the complexing agent lactic acid（HLac） and auxiliary agents citric acid（H3 Cit）, acetic acid（HAc）, and Titriplex Ⅲ have been reported.The effect of pH and lactic acid concentration has been examined. The use of lactic acid as a complexing agent leading to a high extraction of REEs with Cyanex 272 at pH = 5 was compared with systems without lactic acid. The results show that the use of acetic acid along with lactic acid leads to an increase in the extraction percentage of LREEs. While use of citric acid and Titriplex Ⅲ reduces the extraction percentage of LREEs. Finally, the presence of Titriplex Ⅲ together with lactic acid could lead to an increase in the separation factor of Pr and Nd.
基金Project supported by the Basic and Applied Basic Research Project,Guangzhou Basic Research Plan(Grant No.202201011444).
文摘Understanding the photon number statistics of a quantum emitter(QE)interacting with complex photonic environments is fundamental to advances in quantum optics and nanophotonics.We introduce a general theoretical framework for calculating the modal photon number density spectrum(MPNDS)in arbitrary dielectric structures with an embedded two-level QE.We validate our approach by investigating a system composed of a two-level QE and a photonic crystal(PhC)slab with an L3 cavity and a waveguide,finding that the MPNDS exhibits significant changes in both waveguide and background radiative channels as the interaction between the QE and modal field transitions from weak coupling to strong coupling.We observe that the number of photons guided along the waveguide shows a strong dependence on the QE’s transition frequency and transition dipole moment,but demonstrates robustness to the transition dipole moment when the transition frequency approaches the waveguide cutoff frequency.Our work allows for the determination and tailoring of light emission characteristics across diverse radiative channels in complex photonic environments.
基金funded by the National Natural Science Foundation of China (Grant Nos. 52161145404, 61905236, 51961145110)the Fundamental Research Funds for the Central Universities (Grant No. WK2100230020)USTC Research Funds of the Double First-Class Initiative (Grant No. YD3480002002)
文摘In this work,we design and fabricate a deep ultraviolet(DUV)light-emitting array consisting of 10×10 micro-LEDs(μ-LEDs)with each device having 20μm in diameter.Strikingly,the array demonstrates a significant enhancement of total light output power by nearly 52%at the injection current of 100 mA,in comparison to a conventional large LED chip whose emitting area is the same as the array.A much higher(~22%)peak external quantum efficiency,as well as a smaller efficiency droop forμ-LED array,was also achieved.The numerical calculation reveals that the performance boost can be attributed to the higher light extraction efficiency at the edge of eachμ-LED.Additionally,the far-field pattern measurement shows that theμ-LED array possesses a better forward directionality of emission.These findings shed light on the enhancement of the DUV LEDs performance and provide new insights in controlling the light behavior of theμ-LEDs.
基金This work was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China(NSFC)under Grants No.2020YFA0715000 and No.61825402.
文摘We report a feasible method to realize tun able surface plasm on-polarit on(SPP)res onance in orga nic light-emitt ing devices(OLEDs)by emplo ying corrugated Ag-Al alloy electrodes.The excited SPP res onance in duced by the periodic corrugations can be precisely tuned based on the composition ratios of the Ag-Al alloy electrodes.With an appropriate composition ratio of the corrugated alloy electrode,the photons trapped in SPP modes are recovered and extracted effectively.The 25%in creaseme nt in luminance and 21%enhan ceme nt in curre nt efficie ncy have bee n achieved by using the corrugated Ag-Al alloy electrodes in OLEDs.
基金the National Natural Science Foundation of China(Grant No.62104085)the Innovation/Entrepreneurship Program of Jiangsu Province,China(Grant No.JSSCTD202146)。
文摘We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.
基金National Natural Science Foundation of China(No.61071087)Reward Fund of Outstanding Youth and Middle Age Scientist of Shandong Province(No.BS2009N5002)
文摘Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-based blue light LED,the model including deeply etched surface photonic crystals(PhCs)LED is discussed using mode analysis method from light waveguide theory.The distributions of all order modes in GaN layer are obtained by the effective index approximation.The light extraction efficiencies are also calculated by finite-difference time-domain method(FDTD).The emulated results fully coincide with the former analysis.Because the manufacture of the surface photonic crystal is feasible,the work can be very meaningful to design and manufacture the high efficiency GaN-based blue light LED in factory for a large amount.
基金supported by the National Natural Science Foundation of China(No. 51975293)the Aeronautical Science Foundation of China(No. 2019ZD052010)
文摘With the rapid development of the machining and manufacturing industry,welding has been widely used in forming connections of structural parts.At present,manual methods are often used for welding and quality inspection,with low efficiency and unstable product quality.Due to the requirements of visual inspection of weld feature size,a visual inspection system for weld feature size based on line structured light(LSL)is designed and built in this paper.An adaptive light stripe sub-pixel center extraction algorithm and a feature point extraction algorithm for welding light stripe are proposed.The experiment results show that the detection error of the weld width is 0.216 mm,the detection error of the remaining height is 0.035 mm,the single measurement costs 109 ms,and the inspection stability and repeatability of the system is 1%.Our approach can meet the online detection requirements of practical applications.
基金This work was supported by National Key R&D Program of China(2022YFB3605103)the National Natural Science Foundation of China(62204241,U22A2084,62121005,and 61827813)+3 种基金the Natural Science Foundation of Jilin Province(20230101345JC,20230101360JC,and 20230101107JC)the Youth Innovation Promotion Association of CAS(2023223)the Young Elite Scientist Sponsorship Program By CAST(YESS20200182)the CAS Talents Program(E30122E4M0).
文摘240 nm AlGaN-based micro-LEDs with different sizes are designed and fabricated.Then,the external quantum efficiency(EQE)and light extraction efficiency(LEE)are systematically investigated by comparing size and edge effects.Here,it is revealed that the peak optical output power increases by 81.83%with the size shrinking from 50.0 to 25.0μm.Thereinto,the LEE increases by 26.21%and the LEE enhancement mainly comes from the sidewall light extraction.Most notably,transversemagnetic(TM)mode light intensifies faster as the size shrinks due to the tilted mesa side-wall and Al reflector design.However,when it turns to 12.5μm sized micro-LEDs,the output power is lower than 25.0μm sized ones.The underlying mechanism is that even though protected by SiO2 passivation,the edge effect which leads to current leakage and Shockley-Read-Hall(SRH)recombination deteriorates rapidly with the size further shrinking.Moreover,the ratio of the p-contact area to mesa area is much lower,which deteriorates the p-type current spreading at the mesa edge.These findings show a role of thumb for the design of high efficiency micro-LEDs with wavelength below 250 nm,which will pave the way for wide applications of deep ultraviolet(DUV)micro-LEDs.
