A new epitaxial structure of AlGaInP-based light-emitting diode（LED） with a 0.5-μm GaP window layer was fabricated. In addition, indium tin oxide（ITO） and localized Cr deposition beneath the p-pad electrode were ...A new epitaxial structure of AlGaInP-based light-emitting diode（LED） with a 0.5-μm GaP window layer was fabricated. In addition, indium tin oxide（ITO） and localized Cr deposition beneath the p-pad electrode were used as the current spreading layer and the Schottky current blocking layer（CBL）, respectively. The results indicated that ITO and the Schottky CBL improve the total light extraction efficiency by relieving the current density crowding beneath the p-pad electrode. At the current of 20 mA, the light output power of the novel LED was 40% and 19% higher than those of the traditional LED and the new epitaxial LED without CBL. It was also found that the novel LED with ITO and CBL shows better thermal characteristics.展开更多
We present an exact solution to the problem of electromagnetic scattering by nanosphere clusters embedded in a liquid crystal cell, based on the Mie theory. The dependence of the scattering property on the structure p...We present an exact solution to the problem of electromagnetic scattering by nanosphere clusters embedded in a liquid crystal cell, based on the Mie theory. The dependence of the scattering property on the structure parameters is investigated in detail. It is shown that strong transverse light currents at the optical frequency can be obtained from these realized by complex structures. Furthermore, we find that sign reversal of the transverse light current can be changing frequency and voltage. The physical origins of these phenomena have been analyzed. The transverse light current for subwavelength nanoscale dimensions is of practical significance. Thus, the application of these phenomena to optical devices is anticipated.展开更多
To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au （5 nm/5 nm） film deposition. The surface morphology o...To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au （5 nm/5 nm） film deposition. The surface morphology of wafers and the current voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.展开更多
The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a t...The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.展开更多
This paper utilizes multilayer organic light-emitting diodes with a thin layer of dye molecules to study the mech- anism of charge trapping under different electric regimes. It demonstrates that the carrier trapping w...This paper utilizes multilayer organic light-emitting diodes with a thin layer of dye molecules to study the mech- anism of charge trapping under different electric regimes. It demonstrates that the carrier trapping was independent of the current density in devices using fluorescent material as the emitting molecule while this process was exactly opposite when phosphorescent material was used. The triplet-triplet annihilation and dissociation of excitons into free charge carriers was considered to contribute to the decrease in phosphorescent emission under high electric fields. Moreover, the fluorescent dye molecule with a lower energy gap and ionized potential than the host emitter was observed to facilitate the carrier trapping mechanism, and it would produce photon emission.展开更多
We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode （OLED） by using the charge control layers （CCLs） based on Alq3 . The CCLs that are inserted into the emitting layers （EMLs...We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode （OLED） by using the charge control layers （CCLs） based on Alq3 . The CCLs that are inserted into the emitting layers （EMLs） could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device （CD） without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.展开更多
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
Based on the fully dressed confining quark propagator, the pion decay constant fπ, local quark vacuum condensate, and the masses of light quarks and in-medlum Goldstone bosons are investigated. The pion decay constan...Based on the fully dressed confining quark propagator, the pion decay constant fπ, local quark vacuum condensate, and the masses of light quarks and in-medlum Goldstone bosons are investigated. The pion decay constant fπ is predicted and compared with its value of experimental measurement. A great agreement is obtained. With the predicted fπ and values of Goldstone boson masses measured by experiments in free configuration the current masses of light quarks and the masses of in-medium Goldstone bosons are obtained.展开更多
We examine 10 nm thick film structures containing either Hf or Ti sandwiched between two respective oxide layers. The layers are deposited onto heated substrates to create a diffusion region. We observe a high degree ...We examine 10 nm thick film structures containing either Hf or Ti sandwiched between two respective oxide layers. The layers are deposited onto heated substrates to create a diffusion region. We observe a high degree of light sensitivity of the electric current through the film thickness for one polarity of an applied voltage. For the other polarity, the current is not affected by the light. We explain the observed phenomenology using the single-particle model based on the existence of interface states on the metal-oxide interfaces.展开更多
This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with dif...This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with different emitting sizes, we find that there is a similar linear relationship between LED’s 3dB bandwidth and the operation current density. This experiment also shows that high series resistance is one major issue that limits our LED's modulation speed. To further improve the LED bandwidth, the resistance can be reduced by optimizing device layout as well as reducing material bulk resistance. Clearly, this study provides an approach to increase the modulation bandwidth of GaN-based LEDs for VLC systems.展开更多
Silver nanowire（AgNW） networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide（ITO） and have been proposed to replace ITO, which is currently w...Silver nanowire（AgNW） networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide（ITO） and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements.The enhancement ratio of the light output power decreased as the Ga P layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for Ga P layer thicknesses of 0.5 μm, 1 μm, and 8 μm, respectively, when an AgNW network was included in Al Ga In P light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the Ga P layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.展开更多
A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electr...A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.展开更多
The phenomena of acoustic emission in LiNbO3：Fe：Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal i...The phenomena of acoustic emission in LiNbO3：Fe：Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal is modulated by the low frequency acoustic waves. Its frequency increases with the increase of the intensity of incident light and its jump period of breakdown is the same as that of the photovoltaic current Ic, the change of light-induced refractive index △n and the diffracted light intensity L. This phenomenon has been analysed in this paper, which is caused by the inverse piezoelectric strain effect of the jump of space charge field during the quasi-breakdown.展开更多
For the first time the effect of light on the CVC of strained p-n-junction in a strong microwave field is examined. It is shown that the deformation and the microwave field increase the current through p-n-junction, a...For the first time the effect of light on the CVC of strained p-n-junction in a strong microwave field is examined. It is shown that the deformation and the microwave field increase the current through p-n-junction, and the light decreases it. The mechanism of this phenomenon is explained by the fact that under heating of the charge carriers by microwave field the recombination current arises, and under the action of light the generation current arises which are directed oppositely. And under the influence of the deformation the band gap of the semiconductor will be changed.展开更多
It is shown that the increase in the current of an asymmetric p-n-junction, caused by perturbation of potential barrier height and increasing recombination current in a strong microwave field, is suppressed by light g...It is shown that the increase in the current of an asymmetric p-n-junction, caused by perturbation of potential barrier height and increasing recombination current in a strong microwave field, is suppressed by light generated photo carriers, leading to the displacement of current-voltage characteristics of p-n-junction into the direction of smaller current values.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11204009)the Natural Science Foundation of Beijing,China(Grant No.4142005)
文摘A new epitaxial structure of AlGaInP-based light-emitting diode（LED） with a 0.5-μm GaP window layer was fabricated. In addition, indium tin oxide（ITO） and localized Cr deposition beneath the p-pad electrode were used as the current spreading layer and the Schottky current blocking layer（CBL）, respectively. The results indicated that ITO and the Schottky CBL improve the total light extraction efficiency by relieving the current density crowding beneath the p-pad electrode. At the current of 20 mA, the light output power of the novel LED was 40% and 19% higher than those of the traditional LED and the new epitaxial LED without CBL. It was also found that the novel LED with ITO and CBL shows better thermal characteristics.
基金National Key R&D Program of China(2017YFA0303800)National Natural Science Foundation of China(NSFC)(11574031,61421001)
文摘We present an exact solution to the problem of electromagnetic scattering by nanosphere clusters embedded in a liquid crystal cell, based on the Mie theory. The dependence of the scattering property on the structure parameters is investigated in detail. It is shown that strong transverse light currents at the optical frequency can be obtained from these realized by complex structures. Furthermore, we find that sign reversal of the transverse light current can be changing frequency and voltage. The physical origins of these phenomena have been analyzed. The transverse light current for subwavelength nanoscale dimensions is of practical significance. Thus, the application of these phenomena to optical devices is anticipated.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60776047, 60836003, 60476021 and 60576003)
文摘To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au （5 nm/5 nm） film deposition. The surface morphology of wafers and the current voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.
基金Project supported by the National Natural Science Foundation of China(Grant No.10874249)
文摘The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.
基金Project supported by the Key Project of Shanghai Education Committee (Grant No. 08ZZ42)Science and Technology Commission of Shanghai Municipal (Grant Nos. 08PJ14053,08DZ1140702 and 08520511200)
文摘This paper utilizes multilayer organic light-emitting diodes with a thin layer of dye molecules to study the mech- anism of charge trapping under different electric regimes. It demonstrates that the carrier trapping was independent of the current density in devices using fluorescent material as the emitting molecule while this process was exactly opposite when phosphorescent material was used. The triplet-triplet annihilation and dissociation of excitons into free charge carriers was considered to contribute to the decrease in phosphorescent emission under high electric fields. Moreover, the fluorescent dye molecule with a lower energy gap and ionized potential than the host emitter was observed to facilitate the carrier trapping mechanism, and it would produce photon emission.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60906022 and 60676051)the Natural Science Foundation of Tianjin,China (Grant No. 10JCYBJC01100)+2 种基金the Scientific Developing Foundation of Tianjin Education Commission, China (Grant No. 2011ZD02)the Jiangsu Provincial Natural Science Development Foundation for University, China (Grant No. 09KJB140006)the Tianjin Natural Science Council (Grant No. 10SYSYJC28100)
文摘We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode （OLED） by using the charge control layers （CCLs） based on Alq3 . The CCLs that are inserted into the emitting layers （EMLs） could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device （CD） without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.
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.
基金The project supported in part by National Natural Science Foundation of China under Grant Nos. 10247004, 10565001, and the Natural Science Foundation of Guangxi Province of China undcr Grant Nos. 0481030, 0575020, and 0542042
文摘Based on the fully dressed confining quark propagator, the pion decay constant fπ, local quark vacuum condensate, and the masses of light quarks and in-medlum Goldstone bosons are investigated. The pion decay constant fπ is predicted and compared with its value of experimental measurement. A great agreement is obtained. With the predicted fπ and values of Goldstone boson masses measured by experiments in free configuration the current masses of light quarks and the masses of in-medium Goldstone bosons are obtained.
文摘We examine 10 nm thick film structures containing either Hf or Ti sandwiched between two respective oxide layers. The layers are deposited onto heated substrates to create a diffusion region. We observe a high degree of light sensitivity of the electric current through the film thickness for one polarity of an applied voltage. For the other polarity, the current is not affected by the light. We explain the observed phenomenology using the single-particle model based on the existence of interface states on the metal-oxide interfaces.
文摘This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with different emitting sizes, we find that there is a similar linear relationship between LED’s 3dB bandwidth and the operation current density. This experiment also shows that high series resistance is one major issue that limits our LED's modulation speed. To further improve the LED bandwidth, the resistance can be reduced by optimizing device layout as well as reducing material bulk resistance. Clearly, this study provides an approach to increase the modulation bandwidth of GaN-based LEDs for VLC systems.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0400603)the National Natural Science Foundation of China(Grant No.61335004)
文摘Silver nanowire（AgNW） networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide（ITO） and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements.The enhancement ratio of the light output power decreased as the Ga P layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for Ga P layer thicknesses of 0.5 μm, 1 μm, and 8 μm, respectively, when an AgNW network was included in Al Ga In P light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the Ga P layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.
基金supported by the National Natural Science Foundation of China(Grant Nos.61307036 and 61307037)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),Chinathe University Science Research Project of Jiangsu Province,China(Grant No.12KJB510028)
文摘A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.
基金Project supported by the National Natural Science Foundation of China （Grant No 69908003）.
文摘The phenomena of acoustic emission in LiNbO3：Fe：Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal is modulated by the low frequency acoustic waves. Its frequency increases with the increase of the intensity of incident light and its jump period of breakdown is the same as that of the photovoltaic current Ic, the change of light-induced refractive index △n and the diffracted light intensity L. This phenomenon has been analysed in this paper, which is caused by the inverse piezoelectric strain effect of the jump of space charge field during the quasi-breakdown.
文摘For the first time the effect of light on the CVC of strained p-n-junction in a strong microwave field is examined. It is shown that the deformation and the microwave field increase the current through p-n-junction, and the light decreases it. The mechanism of this phenomenon is explained by the fact that under heating of the charge carriers by microwave field the recombination current arises, and under the action of light the generation current arises which are directed oppositely. And under the influence of the deformation the band gap of the semiconductor will be changed.
文摘It is shown that the increase in the current of an asymmetric p-n-junction, caused by perturbation of potential barrier height and increasing recombination current in a strong microwave field, is suppressed by light generated photo carriers, leading to the displacement of current-voltage characteristics of p-n-junction into the direction of smaller current values.
