The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especiall...The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency （EQE） has serious impaction on the internal quantum efficiency （IQE）, because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.展开更多
Photoluminescence(PL) spectra of two different green InGaN/GaN multiple quantum well(MQW) samples S1 and S2,respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyze...Photoluminescence(PL) spectra of two different green InGaN/GaN multiple quantum well(MQW) samples S1 and S2,respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyzed over a wide temperature range of 6 K-3 30 K and an excitation power range of 0.001 mW-75 mW.The excitation power-dependent PL peak energy and linewidth at 6 K show that in an initial excitation power range,the emission process of the MQW is dominated simultaneously by the combined effects of the carrier scattering and Coulomb screening for both the samples,and both the carrier scattering effect and the Coulomb screening effect are stronger for S2 than those for S1;in the highest excitation power range,the emission process of the MQWs is dominated by the filling effect of the high-energy localized states for S1,and by the Coulomb screening effect for S2.The behaviors can be attributed to the fact that sample S2 should have a higher amount of In content in the InGaN well layers than S1 because of the lower growth temperature,and this results in a stronger component fluctuation-induced potential fluctuation and a stronger well/barrier lattice mismatchinduced quantum-confined Stark effect.This explanation is also supported by other relevant measurements of the samples,such as temperature-dependent peak energy and excitation-power-dependent internal quantum efficiency.展开更多
In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, c...In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.展开更多
The optical properties of AlGaN-based quantum well(QW)structure with two coupled thin well layers are investigated by the six-by-six K-P method.Compared with the conventional structure,the new structure,especially the...The optical properties of AlGaN-based quantum well(QW)structure with two coupled thin well layers are investigated by the six-by-six K-P method.Compared with the conventional structure,the new structure,especially the one with lower Al-content in the barrier layer,can enhance the TE-/TM-polarized total spontaneous emission rate due to the strong quantum confinement and wide recombination region.For the conventional QW structure,the reduction of well thickness can lead the degree of polarization(DOP)to decrease and the internal quantum efficiency(IQE)to increase.By using the coupled thin well layers,the DOP for the structure with high Al-content in the barrier layer can be improved,while the DOP will further decrease with low Al-content in the barrier layer.It can be attributed to the band adjustment induced by the combination of barrier height and well layer coupling.The IQE can also be further enhanced to 14.8%-20.5%for various Al-content of barrier layer at J=100 A/cm^(2).In addition,the efficiency droop effect can be expected to be suppressed compared with the conventional structure.展开更多
The performance of InGaN blue light-emitting diodes（LEDs） with different kinds of electron-blocking layers is investigated numerically.We compare the simulated emission spectra,electron and hole concentrations,energ...The performance of InGaN blue light-emitting diodes（LEDs） with different kinds of electron-blocking layers is investigated numerically.We compare the simulated emission spectra,electron and hole concentrations,energy band diagrams,electrostatic fields,and internal quantum efficiencies of the LEDs.The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer（EBL） has a strong spectrum intensity,mitigates efficiency droop,and possesses higher output power compared with the LEDs with the other three types of EBLs.These advantages could be because of the lower electron leakage current and more effective hole injection.The optical performance of the specifically designed LED is also improved in the case of large injection current.展开更多
In this paper, the modeling ofa bifacial polycrystalline silicon solar cells vertical junction is presented. The study in dynamic frequency is limited to wavelengths from 400 nm to 1100 nm. The dependence of solar cel...In this paper, the modeling ofa bifacial polycrystalline silicon solar cells vertical junction is presented. The study in dynamic frequency is limited to wavelengths from 400 nm to 1100 nm. The dependence of solar cell spectral response on wavelengths for several modulation frequencies was evaluated by using solar cell internal quantum efficiency.The objective is to characterize the polycrystalline silicon in 3D. The effect of frequency modulation pulsation on the phase of internal quantum efficiency was presented as well as values of shunt and series resistance for various grains size values. The results show that the value of maximum internal quantum efficiency is about 50% with a wavelength of 0,82 nm and a frequency of 103 rad/s under monochromatic illumination.展开更多
Laser-driven near-infraredⅡ(NIR-Ⅱ)light sources comprising luminescent ceramics represent a promising research frontier,yet their development remains constrained by the external quantum efficiency(EQE)and thermal st...Laser-driven near-infraredⅡ(NIR-Ⅱ)light sources comprising luminescent ceramics represent a promising research frontier,yet their development remains constrained by the external quantum efficiency(EQE)and thermal stability bottleneck of current luminescent materials.Herein,we present a non-equivalent cation substitution strategy to fabricate high-efficiency translucent MgO:Ni^(2+),Cr^(3+)NIR-Ⅱluminescent ceramics.The co-doping of Cr^(3+)induces structural distortion at Ni^(2+)-occupied octahedral sites,effectively breaking the parity-forbidden d-d transition constraint while enabling efficient energy transfer from Cr^(3+)to Ni^(2+).These synergistic effects yield remarkable internal and external quantum efficiencies of 61.06%and 39.69%,respectively.The developed ceramic demonstrates exceptional thermal management capabilities with 31.28 W·m^(−1)·K^(−1)thermal conductivity and 92.11%emission retention at 478 K.When integrated into laser-driven NIR-Ⅱ light sources,the system achieves record-breaking performance of 214 mW output power under 21.43 W/mm^(2)blue laser excitation.Practical demonstrations showcase superior non-destructive imaging capabilities with 5.29 lp/mm spatial resolution and 0.97 contrast ratio.This work establishes a new paradigm for developing high-performance NIR-Ⅱ light sources in advanced imaging and detection technologies.展开更多
A comprehensive design optimization of 1.55-#m high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency （ηi） while maintaining the low internal loss （αi） of the ...A comprehensive design optimization of 1.55-#m high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency （ηi） while maintaining the low internal loss （αi） of the device, thereby achieving high power operation. Four different waveguide structures of broad area lasers were fabricated and characterized in depth. Through theoretical analysis and experiment verifications, we show that laser structures with stepped waveguide and thin upper separate confinement layer will result in high αi and overall slope efficiency. A continuous wave （CW） single side output power of 160 mW was obtained for an uncoated laser with a 50μm active area width and 1 mm cavity length.展开更多
Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Lumine...Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Luminescent iron(III)complexes with low-spin d5 electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer(^(2)MLCT)emission,but little attention has been paid to their application in OLEDs.展开更多
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2006AA03A121)the National Basic Research Program of China(Grant No.2006CB604900)
文摘The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency （EQE） has serious impaction on the internal quantum efficiency （IQE）, because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51672163 and 51872167)the Major Research Plan of the National Natural Science Foundation of China(Grant No.91433112)。
文摘Photoluminescence(PL) spectra of two different green InGaN/GaN multiple quantum well(MQW) samples S1 and S2,respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyzed over a wide temperature range of 6 K-3 30 K and an excitation power range of 0.001 mW-75 mW.The excitation power-dependent PL peak energy and linewidth at 6 K show that in an initial excitation power range,the emission process of the MQW is dominated simultaneously by the combined effects of the carrier scattering and Coulomb screening for both the samples,and both the carrier scattering effect and the Coulomb screening effect are stronger for S2 than those for S1;in the highest excitation power range,the emission process of the MQWs is dominated by the filling effect of the high-energy localized states for S1,and by the Coulomb screening effect for S2.The behaviors can be attributed to the fact that sample S2 should have a higher amount of In content in the InGaN well layers than S1 because of the lower growth temperature,and this results in a stronger component fluctuation-induced potential fluctuation and a stronger well/barrier lattice mismatchinduced quantum-confined Stark effect.This explanation is also supported by other relevant measurements of the samples,such as temperature-dependent peak energy and excitation-power-dependent internal quantum efficiency.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1034004 and 50825603)the Fundamental Research Funds for the Central Universities,China(Grant Nos.12QX14 and 11ZG01)
文摘In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.
基金Project supported by the National Natural Science Foundation of China(Grant No.61874168)the Jiangsu Province I-U-R Cooperation Project,China(Grant No.BY2019114)the Nantong Science and Technology Project,China(Grant No.JC2019006)。
文摘The optical properties of AlGaN-based quantum well(QW)structure with two coupled thin well layers are investigated by the six-by-six K-P method.Compared with the conventional structure,the new structure,especially the one with lower Al-content in the barrier layer,can enhance the TE-/TM-polarized total spontaneous emission rate due to the strong quantum confinement and wide recombination region.For the conventional QW structure,the reduction of well thickness can lead the degree of polarization(DOP)to decrease and the internal quantum efficiency(IQE)to increase.By using the coupled thin well layers,the DOP for the structure with high Al-content in the barrier layer can be improved,while the DOP will further decrease with low Al-content in the barrier layer.It can be attributed to the band adjustment induced by the combination of barrier height and well layer coupling.The IQE can also be further enhanced to 14.8%-20.5%for various Al-content of barrier layer at J=100 A/cm^(2).In addition,the efficiency droop effect can be expected to be suppressed compared with the conventional structure.
基金Project supported by the National Natural Science Foundation of China(Grant No.61176043)the Fund for Strategic and Emerging Industries of Guangdong Province,China(Grant No.2010A081002005)the Project of Combination of Production and Research of the Education Ministry and Guangdong Province,China(Grant No.2010B090400192)
文摘The performance of InGaN blue light-emitting diodes（LEDs） with different kinds of electron-blocking layers is investigated numerically.We compare the simulated emission spectra,electron and hole concentrations,energy band diagrams,electrostatic fields,and internal quantum efficiencies of the LEDs.The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer（EBL） has a strong spectrum intensity,mitigates efficiency droop,and possesses higher output power compared with the LEDs with the other three types of EBLs.These advantages could be because of the lower electron leakage current and more effective hole injection.The optical performance of the specifically designed LED is also improved in the case of large injection current.
文摘In this paper, the modeling ofa bifacial polycrystalline silicon solar cells vertical junction is presented. The study in dynamic frequency is limited to wavelengths from 400 nm to 1100 nm. The dependence of solar cell spectral response on wavelengths for several modulation frequencies was evaluated by using solar cell internal quantum efficiency.The objective is to characterize the polycrystalline silicon in 3D. The effect of frequency modulation pulsation on the phase of internal quantum efficiency was presented as well as values of shunt and series resistance for various grains size values. The results show that the value of maximum internal quantum efficiency is about 50% with a wavelength of 0,82 nm and a frequency of 103 rad/s under monochromatic illumination.
基金financially supported by the Joint Funds of the National Natural Science Foundation of China and Chongqing(U24A2056)the National Key R&D Program of China(2023YFB3506600 and 2023YFB3506602)the University Key Laboratory of Guangdong(2024KSYS021).
文摘Laser-driven near-infraredⅡ(NIR-Ⅱ)light sources comprising luminescent ceramics represent a promising research frontier,yet their development remains constrained by the external quantum efficiency(EQE)and thermal stability bottleneck of current luminescent materials.Herein,we present a non-equivalent cation substitution strategy to fabricate high-efficiency translucent MgO:Ni^(2+),Cr^(3+)NIR-Ⅱluminescent ceramics.The co-doping of Cr^(3+)induces structural distortion at Ni^(2+)-occupied octahedral sites,effectively breaking the parity-forbidden d-d transition constraint while enabling efficient energy transfer from Cr^(3+)to Ni^(2+).These synergistic effects yield remarkable internal and external quantum efficiencies of 61.06%and 39.69%,respectively.The developed ceramic demonstrates exceptional thermal management capabilities with 31.28 W·m^(−1)·K^(−1)thermal conductivity and 92.11%emission retention at 478 K.When integrated into laser-driven NIR-Ⅱ light sources,the system achieves record-breaking performance of 214 mW output power under 21.43 W/mm^(2)blue laser excitation.Practical demonstrations showcase superior non-destructive imaging capabilities with 5.29 lp/mm spatial resolution and 0.97 contrast ratio.This work establishes a new paradigm for developing high-performance NIR-Ⅱ light sources in advanced imaging and detection technologies.
基金Project supported by the National Natural Science Foundation of China(Nos.61274046,61201103)the National High Technology Research and Development Program of China(No.2013AA014202)
文摘A comprehensive design optimization of 1.55-#m high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency （ηi） while maintaining the low internal loss （αi） of the device, thereby achieving high power operation. Four different waveguide structures of broad area lasers were fabricated and characterized in depth. Through theoretical analysis and experiment verifications, we show that laser structures with stepped waveguide and thin upper separate confinement layer will result in high αi and overall slope efficiency. A continuous wave （CW） single side output power of 160 mW was obtained for an uncoated laser with a 50μm active area width and 1 mm cavity length.
基金from the National Natural Science Foundation of China(grant nos.51925303 and 91833304)the Program for JLU Science and Technology Innovative Research Team of China(JLUSTIRTgrant no.2019TD-33).
文摘Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Luminescent iron(III)complexes with low-spin d5 electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer(^(2)MLCT)emission,but little attention has been paid to their application in OLEDs.
