We have synthesized Ca2Si5N8：Eu^2＋ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that...We have synthesized Ca2Si5N8：Eu^2＋ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8：Eu^2＋ phosphor shows a broad red emission band centred at -1.97 eV-2.01 eV. The gravity centre of the excitation band is located at 3.0 eV 3.31 eV. The centroid shift of the 5d levels of Eu^2＋ is determined to be -1.17 eV, and the red-shift of the lowest absorption band to be - 0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang-Rhys parameter S = 6.0, the phonon energy hv = 52 meV, and the Stokes shift △S = 0.57 eV are obtained. The emission intensity maximum occurring at -200 K can be explained by a trapping effect. Both photoluminescence （PL） emission intensity and decay time decrease with temperature increasing beyond 200 K due to the non-radiative process.展开更多
Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically,...Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency （IQE）. The results indicate that LEDs with an n-AIGaN HBL with gradual AI composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conven tional p-A1GaN EBL or a common n-A1GaN HBL. Meanwhile, the efficiency droop is alleviated when an n-A1GaN HBL with gradual A1 composition is used.展开更多
The novel AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) with double superlattice structure(DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-peri...The novel AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) with double superlattice structure(DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-period Mg modulation-doped p-AlGaN/u-GaN superlattice(SL) and 4-period p-AlGaN/p-GaN SL electron blocking layer, which are used to replace the p-type GaN layer and electron blocking layer of conventional UV-LEDs, respectively. Due to the special effects and interfacial stress, the AlGaN/GaN short-period superlattice can reduce the acceptor ionization energy of the ptype regions, thereby increasing the hole concentration. Meanwhile, the multi-barrier electron blocking layers are effective in suppressing electron leakage and improving hole injection. Experimental results show that the enhancements of 22.5%and 37.9% in the output power and external quantum efficiency at 120 m A appear in the device with double superlattice structure.展开更多
A new method for patterned sapphire substrate （PSS） design is developed and proven to be reliable and cost-effective. As progress is made with LEDs＇ luminous efficiency, the pattern units of PSS become more complic...A new method for patterned sapphire substrate （PSS） design is developed and proven to be reliable and cost-effective. As progress is made with LEDs＇ luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs＇ light extraction efficiency （LEE）. Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years.展开更多
The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior opt...The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power, a reduction in current leakage and alleviation of efficiency droop. These improvements can be attributed to the p-InA1GaN serving as hole injection layers, which can alleviate the band bending induced by the polarization field, thereby improving both the hole injection efficiency and the electron blocking efficiency.展开更多
Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red...Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red and green PeLEDs,blue PeLEDs have not been extensively investigated,which limits their commercial applications in the fields of luminance and full-color displays.In this review,blue-PeLED-related research is categorized by the composition of perovskite.The main challenges and corresponding optimization strategies for perovskite films are summarized.Next,the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers.Accordingly,future directions for blue PeLEDs are discussed.This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs,thereby enhancing their development and application scope.展开更多
Progress with GaN-based light emitting diodes （LEDs） that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow...Progress with GaN-based light emitting diodes （LEDs） that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an A1N template layer for deep-ultraviolet （DUV） LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostruc- tures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostruc- tures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.展开更多
We use a simple and controllable method to fabricate GaN-based light-emitting diodes （LEDs） with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching （...We use a simple and controllable method to fabricate GaN-based light-emitting diodes （LEDs） with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching （ICP-RIE）. Our exper- iment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 rnW under a 20-mA current injection, 6.75% higher than 32.6 mW, the output powers of the conventional LEDs under the same current injection.展开更多
The relationship between the photometric, electric, and thermal parameters of light-emitting diodes（LEDs） is important for optimizing the LED illumination design. Indium gallium aluminium phosphide（InGaAlP）-based ...The relationship between the photometric, electric, and thermal parameters of light-emitting diodes（LEDs） is important for optimizing the LED illumination design. Indium gallium aluminium phosphide（InGaAlP）-based thin-film surface-mounted device（SMD） LEDs have attracted wide attention in research and development due to their portability and miniaturization. We report the optical characterization of InGaAlP thin-film SMD LED mounted on FR4, 2 W, and 5 W aluminum（Al） packages. The optical and thermal parameters of LED are determined at different injection currents and ambient temperatures by combining the T3ster（thermal transient tester） and TeraL ED（thermal and radiometric characterization of power LEDs） systems. Analysis shows that LED on a 5 W Al substrate package obtains the highest luminous and optical efficiency.展开更多
Wafer-scale SiO2 photonic crystal （PhC） patterns （SiO2 air-hole PhC, SiO2-pillar PhC） on indium tin oxide （ITO） layer of GaN-based light-emitting diode （LED） are fabricated via novel nanospherical-lens lithogr...Wafer-scale SiO2 photonic crystal （PhC） patterns （SiO2 air-hole PhC, SiO2-pillar PhC） on indium tin oxide （ITO） layer of GaN-based light-emitting diode （LED） are fabricated via novel nanospherical-lens lithography. Nanoscale polystyrene spheres are self-assembled into a hexagonal closed-packed monolayer array acting as convex lens for expo- sure using conventional lithography instrument. The light output power is enhanced by as great as 40.5% and 61% over those of as-grown LEDs, for SiO2-hole PhC and SiO2-pillar PhC LEDs, respectively. No degradation to LED electrical properties is found due to the fact that SiO2 PhC structures are fabricated on ITO current spreading electrode. For SiO2- pillar PhC LEDs, which have the largest light output power in all LEDs, no dry etching, which would introduce etching damage, was involved. Our method is demonstrated to be a simple, low cost, and high-yield technique for fabricating the PhC LEDs. Furthermore, the finite difference time domain simulation is also performed to further reveal the emission characteristics of LEDs with PhC structures.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 50672007)Program for the New Century Excellent Talents of China (Grant No NCET-06-0082)the National Basic Research Program of China (Grant No2007CB936202)
文摘We have synthesized Ca2Si5N8：Eu^2＋ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8：Eu^2＋ phosphor shows a broad red emission band centred at -1.97 eV-2.01 eV. The gravity centre of the excitation band is located at 3.0 eV 3.31 eV. The centroid shift of the 5d levels of Eu^2＋ is determined to be -1.17 eV, and the red-shift of the lowest absorption band to be - 0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang-Rhys parameter S = 6.0, the phonon energy hv = 52 meV, and the Stokes shift △S = 0.57 eV are obtained. The emission intensity maximum occurring at -200 K can be explained by a trapping effect. Both photoluminescence （PL） emission intensity and decay time decrease with temperature increasing beyond 200 K due to the non-radiative process.
基金supported by the National Natural Science Foundation of China(Grant No.61176043)the Special Funds for Provincial Strategic and Emerging Industries Projects of Guangdong Province,China(Grant Nos.2010A081002005,2011A081301003,and 2012A080304016)the Youth Foundation of South China Normal University(Grant No.2012KJ018)
文摘Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency （IQE）. The results indicate that LEDs with an n-AIGaN HBL with gradual AI composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conven tional p-A1GaN EBL or a common n-A1GaN HBL. Meanwhile, the efficiency droop is alleviated when an n-A1GaN HBL with gradual A1 composition is used.
基金supported by the National Key R&D Program of China(Grant Nos.2016YFB0400800,2016YFB0400801,and 2016YFB0400802)the National Natural Science Foundation of China(Grant No.61634005)the Fundamental Research Funds for the Central Universities,China(Grant No.JBZ171101)
文摘The novel AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) with double superlattice structure(DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-period Mg modulation-doped p-AlGaN/u-GaN superlattice(SL) and 4-period p-AlGaN/p-GaN SL electron blocking layer, which are used to replace the p-type GaN layer and electron blocking layer of conventional UV-LEDs, respectively. Due to the special effects and interfacial stress, the AlGaN/GaN short-period superlattice can reduce the acceptor ionization energy of the ptype regions, thereby increasing the hole concentration. Meanwhile, the multi-barrier electron blocking layers are effective in suppressing electron leakage and improving hole injection. Experimental results show that the enhancements of 22.5%and 37.9% in the output power and external quantum efficiency at 120 m A appear in the device with double superlattice structure.
基金Project supported by the National Natural Science Fundation for Excellent Young Scholars of China(Grant No.51422203)the National Natural Science Foundation of China(Grant No.51372001)+1 种基金the Outstanding Youth Foundation of Guangdong Scientific Committee(Grant No.S2013050013882)the Strategic Special Funds for LEDs of Guangdong Province,China(Grant Nos.2011A081301010,2011A081301012,2012A080302002,and 2012A080302004)
文摘A new method for patterned sapphire substrate （PSS） design is developed and proven to be reliable and cost-effective. As progress is made with LEDs＇ luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs＇ light extraction efficiency （LEE）. Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years.
基金Project supported by the National Natural Science Foundation of China (Grant No.61176043)the Special Funds for Strategic and Emerging Industries Projects of Guangdong Province,China (Grant Nos.2010A081002005,2011A081301003,and 2012A080304016)
文摘The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power, a reduction in current leakage and alleviation of efficiency droop. These improvements can be attributed to the p-InA1GaN serving as hole injection layers, which can alleviate the band bending induced by the polarization field, thereby improving both the hole injection efficiency and the electron blocking efficiency.
基金This work was supported by the National Natural Science Foundation of China(51775199,51735004)Natural Science Foundation of Guangdong Province(2018B030306008)the Fundamental Research Funds for the Central Universities.
文摘Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red and green PeLEDs,blue PeLEDs have not been extensively investigated,which limits their commercial applications in the fields of luminance and full-color displays.In this review,blue-PeLED-related research is categorized by the composition of perovskite.The main challenges and corresponding optimization strategies for perovskite films are summarized.Next,the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers.Accordingly,future directions for blue PeLEDs are discussed.This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs,thereby enhancing their development and application scope.
基金Project supported by the National Natural Science Foundation of China(Grant No.61334009)the National High Technology Research and Development Program of China(Grant Nos.2015AA03A101 and 2014BAK02B08)+1 种基金China International Science and Technology Cooperation Program(Grant No.2014DFG62280)the"Import Outstanding Technical Talent Plan"and"Youth Innovation Promotion Association Program"of the Chinese Academy of Sciences
文摘Progress with GaN-based light emitting diodes （LEDs） that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an A1N template layer for deep-ultraviolet （DUV） LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostruc- tures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostruc- tures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.
基金Project supported by the National High Technology Research and Development Program of China (Grant Nos.2011AA03A112,2011AA03A106,and 2013AA03A101)the National Natural Science Foundation of China (Grant Nos.11204360,61210014,and 61078046)+2 种基金the Science and Technology Innovation Program of Department of Education of Guangdong Province,China (Grant No.2012CXZD0017)the Industry–Academia Research Union Special Fund of Guangdong Province,China (Grant No.2012B091000169)the Science and Technology Innovation Platform of Industry–Academia Research Union of Guangdong Province–Ministry Cooperation Special Fund,China (Grant No.2012B090600038)
文摘We use a simple and controllable method to fabricate GaN-based light-emitting diodes （LEDs） with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching （ICP-RIE）. Our exper- iment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 rnW under a 20-mA current injection, 6.75% higher than 32.6 mW, the output powers of the conventional LEDs under the same current injection.
文摘The relationship between the photometric, electric, and thermal parameters of light-emitting diodes（LEDs） is important for optimizing the LED illumination design. Indium gallium aluminium phosphide（InGaAlP）-based thin-film surface-mounted device（SMD） LEDs have attracted wide attention in research and development due to their portability and miniaturization. We report the optical characterization of InGaAlP thin-film SMD LED mounted on FR4, 2 W, and 5 W aluminum（Al） packages. The optical and thermal parameters of LED are determined at different injection currents and ambient temperatures by combining the T3ster（thermal transient tester） and TeraL ED（thermal and radiometric characterization of power LEDs） systems. Analysis shows that LED on a 5 W Al substrate package obtains the highest luminous and optical efficiency.
基金Project supported by the National Basic Research Program of China (Grant No.2011CB301902)
文摘Wafer-scale SiO2 photonic crystal （PhC） patterns （SiO2 air-hole PhC, SiO2-pillar PhC） on indium tin oxide （ITO） layer of GaN-based light-emitting diode （LED） are fabricated via novel nanospherical-lens lithography. Nanoscale polystyrene spheres are self-assembled into a hexagonal closed-packed monolayer array acting as convex lens for expo- sure using conventional lithography instrument. The light output power is enhanced by as great as 40.5% and 61% over those of as-grown LEDs, for SiO2-hole PhC and SiO2-pillar PhC LEDs, respectively. No degradation to LED electrical properties is found due to the fact that SiO2 PhC structures are fabricated on ITO current spreading electrode. For SiO2- pillar PhC LEDs, which have the largest light output power in all LEDs, no dry etching, which would introduce etching damage, was involved. Our method is demonstrated to be a simple, low cost, and high-yield technique for fabricating the PhC LEDs. Furthermore, the finite difference time domain simulation is also performed to further reveal the emission characteristics of LEDs with PhC structures.
