The efficiency droop behaviors of GaN-based green light-emitting diodes (LEDs) are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as te...The efficiency droop behaviors of GaN-based green light-emitting diodes (LEDs) are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level (1 A/cm2 ) with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs.展开更多
Gallium nitride (GaN) based light-emitting diodes (LEDs) with chirped multiple quantum well (MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs wit...Gallium nitride (GaN) based light-emitting diodes (LEDs) with chirped multiple quantum well (MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells (QWs), LEDs with chirped MQW structures have better internal quantum efficiency (IQE) and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 mA/mm2, reduced down from 28.6% (conventional uniform LEDs) to 23.7% (chirped MQWs-a) and 18.6% (chirped MQWs-b), respectively. Meanwhile, the peak IQE increases from 76.9% (uniform LEDs) to 83.7% (chirped MQWs-a) and 88.6% (chirped MQWs-b). The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop.展开更多
The InGaN/GaN blue light emitting diode(LED) is numerically investigated using a triangular-shaped quantum well model,which involves analysis on its energy band,carrier concentration,overlap of electron and hole wav...The InGaN/GaN blue light emitting diode(LED) is numerically investigated using a triangular-shaped quantum well model,which involves analysis on its energy band,carrier concentration,overlap of electron and hole wave functions,radiative recombination rate,and internal quantum efficiency.The simulation results reveal that the InGaN/GaN blue light emitting diode with triangular quantum wells exhibits a higher radiative recombination rate than the conventional light emitting diode with rectangular quantum wells due to the enhanced overlap of electron and hole wave functions(above 90%) under the polarization field.Consequently,the efficiency droop is only 18% in the light emitting diode with triangular-shaped quantum wells,which is three times lower than that in a conventional LED.展开更多
In GaN/GaN multiple quantum well(MQW) green light-emitting diodes(LEDs) with varying In GaN quantum well layer thickness are fabricated and characterized. The investigation of luminescence efficiency versus inject...In GaN/GaN multiple quantum well(MQW) green light-emitting diodes(LEDs) with varying In GaN quantum well layer thickness are fabricated and characterized. The investigation of luminescence efficiency versus injection current reveals that several physical mechanisms may jointly influence the efficiency droop, resulting in a non-monotonic variation of droop behavior with increasing quantum well(QW) thickness. When the QW is very thin, the increase of In GaN well layer thickness makes the efficiency droop more serious due to the enhancement of polarization effect. When the QW thickness increases further, however, the droop is alleviated significantly, which is mainly ascribed to the enhanced nonradiative recombination process and the weak delocalization effect.展开更多
Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated,with the In composition in each well layer(WL)alon...Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated,with the In composition in each well layer(WL)along the growth direction progressively increasing for SA and progressively decreasing for SB.The results show that SB exhibits an improved efficiency droop compared with SA.This phenomenon can be explained as follows:owing to the difference in growth pattern of the WL between these two samples,the terminal region of the WL in SB contains fewer In atoms than in SA,and therefore the former undergoes less In volatilization than the latter during the waiting period required for warming-up due to the difference in the growth temperature between well and barrier layers.This results in SB having a deeper triangular-shaped potential well in its WL than SA,which strongly confines the carriers to the initial region of the WL to prevent them from leaking to the p-GaN side,thus improving the efficiency droop.Moreover,the improvement in the efficiency droop for SB is also partly attributed to its stronger Coulomb screening effect and carrier localization effect.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
InGaN-based green light-emitting diodes (LEDs) with different growth temperatures of superlattice grown on Si (111) substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. ...InGaN-based green light-emitting diodes (LEDs) with different growth temperatures of superlattice grown on Si (111) substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. It is observed that with the decrease of the growth temperature of the superlattice from 895℃ to 855℃, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures (about 100 K-150 K). Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.展开更多
In this study, the efficiency droop of an InGaN light-emitting diode (LED) is reduced slgnlncanUy oy using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the d...In this study, the efficiency droop of an InGaN light-emitting diode (LED) is reduced slgnlncanUy oy using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency, which is revealed by investigating the light currents, internal quantum efficiencies, energy band diagrams, carrier concentrations, carrier current densities, and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device (APSYS).展开更多
In this study, an InGaN lighting-emitting diode (LED) containing GaN/A1GaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and r...In this study, an InGaN lighting-emitting diode (LED) containing GaN/A1GaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and radiative recombination rate indicate that the proposed LED has a higher output power and an internal quantum efficiency, and a lower efficiency droop than the LED containing conventional GaN or A1GaN barriers. These improvements mainly arise from the modified energy bands, which is evidenced by analyzing the LED energy band diagram and electrostatic field near the active region. The modified energy bands effectively improve carrier injection and confinement, which significantly reduces electron leakage and increases the rate of radiative recombination in the quantum wells.展开更多
The advantages of a GaN-AlGaN-InGaN last quantum barrier (LQB) in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, highe...The advantages of a GaN-AlGaN-InGaN last quantum barrier (LQB) in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, higher recombi- nation rate, and less efficiency droop compared with conventional GaN LQBs. These improvements in the electrical and optical characteristics are attributed mainly to the specially designed GaN-AlGaN-InGaN LQB, which enhances electron confinement and improves hole injection efficiency.展开更多
The optical and physical properties of an InGaN light-emitting diode (LED) with a specific design of a staggered AlGaN electron-blocking layer (EBL) are investigated numerically in detail. The electrostatic field ...The optical and physical properties of an InGaN light-emitting diode (LED) with a specific design of a staggered AlGaN electron-blocking layer (EBL) are investigated numerically in detail. The electrostatic field distribution, energy band, carrier concentration, electroluminescence (EL) intensity, internal quantum efficiency (IQE), and the output power are simulated. The results reveal that this specific design has a remarkable improvement in optical performance compared with the design of a conventional LED. The lower electron leakage current, higher hole injection efficiency, and consequently mitigated efficiency droop are achieved. The significant decrease of electrostatic field at the interface between the last barrier and the EBL of the LED could be one of the main reasons for these improvements.展开更多
A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes (LEDs). The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the ...A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes (LEDs). The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional A1GaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.展开更多
InGaN/AIlnGaN superlattice (SL) is designed as the electron blocking layer (EBL) of an InGaN/GaN-based light- emitting diode (LED). The energy band structure, polarization field at the last-GaN-barrier/EBL inter...InGaN/AIlnGaN superlattice (SL) is designed as the electron blocking layer (EBL) of an InGaN/GaN-based light- emitting diode (LED). The energy band structure, polarization field at the last-GaN-barrier/EBL interface, carrier concen- tration, radiative recombination rate, electron leakage, internal quantum efficiency (IQE), current-voltage (l-V) perfor- mance curve, light output-current (L-l) characteristic, and spontaneous emission spectrum are systematically numerically investigated using APSYS simulation software. It is found that the fabricated LED with InGaN/AIInGaN SL EBL exhibits higher light output power, low forward voltage, and low current leakage compared with those of its counterparts. Meanwhile, the efficiency droop can be effectively mitigated. These improvements are mainly attributed to the higher hole injection efficiency and better electron confinement when InGaN/AIlnGaN SL EBL is used.展开更多
P-InGaN/p-GaN superlattices (SLs) are developed for a hole accumulation layer (HAL) of a blue light emitting diode (LED). Free hole concentration as high as 2.6× 1018 cm-3 is achieved by adjusting the Cp2Mg...P-InGaN/p-GaN superlattices (SLs) are developed for a hole accumulation layer (HAL) of a blue light emitting diode (LED). Free hole concentration as high as 2.6× 1018 cm-3 is achieved by adjusting the Cp2Mg flow rate during the growth of p-InGaN/p-GaN SLs. The p-InGaN/p-GaN SLs with appropriate Cp2Mg flow rates are then incorporated between the multi-quantum well and A1GaN electron blocking layer as an HAL, which leads to the enhancement of light output power by 29% at 200 mA, compared with the traditional LED without such SL HAL. Meanwhile, the efficiency droop is also effectively alleviated in the LED with the SL HAL. The improved performance is attributed to the increased hole injection efficiency, and the reduced electron leakage by inserting the p-type SL HAL.展开更多
The characteristics of a blue light-emitting diode (LED) with an AIlnN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carder concentrations in the quantum wells, energy band di...The characteristics of a blue light-emitting diode (LED) with an AIlnN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carder concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AIInN/GaN SL EBL has better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region than the LED with a conventional rectangular AIGaN EBL or a A1GaN/GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.展开更多
The efficiency enhancement of an InGaN light-emitting diode (LED) with an A1GaN/InGaN superlattice (SL) electron-blocking layer (EBL) is studied numerically, which involves the light-current performance curve, i...The efficiency enhancement of an InGaN light-emitting diode (LED) with an A1GaN/InGaN superlattice (SL) electron-blocking layer (EBL) is studied numerically, which involves the light-current performance curve, internal quan- tum efficiency electrostatic field band wavefunction, energy band diagram carrier concentration, electron current density, and radiative recombination rate. The simulation results indicate that the LED with an A1GaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular A1GaN EBL or a normal A1GaN/GaN SL EBL because of the appropriately modified energy band diagram, which is favorable ibr the injection of holes and confinement of elec- trons. Additionally, the efficiency droop of the LED with an AIGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.展开更多
The characteristics ofnitride-based blue light-emitting diodes (LEDs) with A1GaN composition-graded barriers are analyzed numerically. The carrier concentrations in the quantum wells (QWs), the energy band di- agr...The characteristics ofnitride-based blue light-emitting diodes (LEDs) with A1GaN composition-graded barriers are analyzed numerically. The carrier concentrations in the quantum wells (QWs), the energy band di- agrams, the electrostatic fields, and the light output power are investigated by APSYS software. The simulation results show that the LED with AlGaN composition-graded barriers has a better performance than its AlGaN/InGaN counterpart owing to the increase of hole injection and the enhancement of electron confinement. The simulation results also suggest that the output power is enhanced significantly and the efficiency droop is markedly improved when the AIGaN barriers are replaced by AlGaN composition-graded barriers.展开更多
基金Project supported by the State Key Program for Basic Research of China (Grant Nos. 2010CB327504, 2011CB301900, and 2011CB922100)the National Natural Science Foundation of China (Grant Nos. 60825401, 60936004, and 11104130)the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK2012110, BK2011556, and BK2011050)
文摘The efficiency droop behaviors of GaN-based green light-emitting diodes (LEDs) are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level (1 A/cm2 ) with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs.
基金supported by the National High Technology Research and Development Program of China(Grant No.2014AA032608)the Key Laboratory for Mechanical Behavior of Material of Xi’an Jiaotong University,China(Grant No.20121201)the Fundamental Research Funds for the Central Universities,China
文摘Gallium nitride (GaN) based light-emitting diodes (LEDs) with chirped multiple quantum well (MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells (QWs), LEDs with chirped MQW structures have better internal quantum efficiency (IQE) and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 mA/mm2, reduced down from 28.6% (conventional uniform LEDs) to 23.7% (chirped MQWs-a) and 18.6% (chirped MQWs-b), respectively. Meanwhile, the peak IQE increases from 76.9% (uniform LEDs) to 83.7% (chirped MQWs-a) and 88.6% (chirped MQWs-b). The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61076013,51102003,and 60990313)the National Basic Research Program of China (Grant No. 2012CB619304)the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20100001120014)
文摘The InGaN/GaN blue light emitting diode(LED) is numerically investigated using a triangular-shaped quantum well model,which involves analysis on its energy band,carrier concentration,overlap of electron and hole wave functions,radiative recombination rate,and internal quantum efficiency.The simulation results reveal that the InGaN/GaN blue light emitting diode with triangular quantum wells exhibits a higher radiative recombination rate than the conventional light emitting diode with rectangular quantum wells due to the enhanced overlap of electron and hole wave functions(above 90%) under the polarization field.Consequently,the efficiency droop is only 18% in the light emitting diode with triangular-shaped quantum wells,which is three times lower than that in a conventional LED.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.6157413561574134+12 种基金6147414261474110613770206137608961223005and 61321063)the One-Hundred Person Project of the Chinese Academy of Sciencesthe Basic Research Project of Jiangsu ProvinceChina(Grant No.BK20130362)the Scientific Research Fund of Chongqing Municipal Education CommissionChina(Grant No.KJ131206)the Natural Science Foundation of Chongqing Municipal Science and Technology CommissionChina(Grant No.cstc2012jj A50036)
文摘In GaN/GaN multiple quantum well(MQW) green light-emitting diodes(LEDs) with varying In GaN quantum well layer thickness are fabricated and characterized. The investigation of luminescence efficiency versus injection current reveals that several physical mechanisms may jointly influence the efficiency droop, resulting in a non-monotonic variation of droop behavior with increasing quantum well(QW) thickness. When the QW is very thin, the increase of In GaN well layer thickness makes the efficiency droop more serious due to the enhancement of polarization effect. When the QW thickness increases further, however, the droop is alleviated significantly, which is mainly ascribed to the enhanced nonradiative recombination process and the weak delocalization effect.
基金the National Natural Science Foundation of China(Grant Nos.51872167 and 51672163)the Major Science and Technology Innovation Project of Shandong Province,China(Grant No.2019JZZY010210).
文摘Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated,with the In composition in each well layer(WL)along the growth direction progressively increasing for SA and progressively decreasing for SB.The results show that SB exhibits an improved efficiency droop compared with SA.This phenomenon can be explained as follows:owing to the difference in growth pattern of the WL between these two samples,the terminal region of the WL in SB contains fewer In atoms than in SA,and therefore the former undergoes less In volatilization than the latter during the waiting period required for warming-up due to the difference in the growth temperature between well and barrier layers.This results in SB having a deeper triangular-shaped potential well in its WL than SA,which strongly confines the carriers to the initial region of the WL to prevent them from leaking to the p-GaN side,thus improving the efficiency droop.Moreover,the improvement in the efficiency droop for SB is also partly attributed to its stronger Coulomb screening effect and carrier localization effect.
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Supported by the National Natural Science Foundation of China under Grant No 61334001the National Key Research and Development Program of China under Grant Nos 2016YFB0400600,2016YFB0400601 and 2016YFB0400100+1 种基金the National Science Foundation for Young Scientists of China under Grant No 21405076the Fund for Less Developed Regions of the National Natural Science Foundation of China under Grant No 11364034
文摘InGaN-based green light-emitting diodes (LEDs) with different growth temperatures of superlattice grown on Si (111) substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. It is observed that with the decrease of the growth temperature of the superlattice from 895℃ to 855℃, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures (about 100 K-150 K). Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.
基金Project 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)+2 种基金the First Phase of Construction of Guangdong Research Institute of Semiconductor Lighting Industrial Technology,China(Grant No.2010A081001001)the High Efficiency LED Epitaxy and Chip Structure and Key Technology for Industrialization,China(Grant No.2012A080302002)the Youth Funding of South China Normal University(Grant No.2012KJ018)
文摘In this study, the efficiency droop of an InGaN light-emitting diode (LED) is reduced slgnlncanUy oy using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency, which is revealed by investigating the light currents, internal quantum efficiencies, energy band diagrams, carrier concentrations, carrier current densities, and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device (APSYS).
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFB0403100 and 2017YFB0403101)the National Natural Science Foundation of China(Grant Nos.61404114,61504119,and 11004170)+1 种基金the China Postdoctoral Science Foundation(Grant No.2017M611923)the Jiangsu Planned Projects for Postdoctoral Research Funds,China(Grant No.1701067B)
文摘In this study, an InGaN lighting-emitting diode (LED) containing GaN/A1GaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and radiative recombination rate indicate that the proposed LED has a higher output power and an internal quantum efficiency, and a lower efficiency droop than the LED containing conventional GaN or A1GaN barriers. These improvements mainly arise from the modified energy bands, which is evidenced by analyzing the LED energy band diagram and electrostatic field near the active region. The modified energy bands effectively improve carrier injection and confinement, which significantly reduces electron leakage and increases the rate of radiative recombination in the quantum wells.
基金Project supported by the Special Strategic Emerging Industries of Guangdong Province,China(Grant Nos.2011A081301004 and 2012A080304006)
文摘The advantages of a GaN-AlGaN-InGaN last quantum barrier (LQB) in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, higher recombi- nation rate, and less efficiency droop compared with conventional GaN LQBs. These improvements in the electrical and optical characteristics are attributed mainly to the specially designed GaN-AlGaN-InGaN LQB, which enhances electron confinement and improves hole injection efficiency.
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 Guided by Ministry of Education, China (Grant No. 2010B090400192)
文摘The optical and physical properties of an InGaN light-emitting diode (LED) with a specific design of a staggered AlGaN electron-blocking layer (EBL) are investigated numerically in detail. The electrostatic field distribution, energy band, carrier concentration, electroluminescence (EL) intensity, internal quantum efficiency (IQE), and the output power are simulated. The results reveal that this specific design has a remarkable improvement in optical performance compared with the design of a conventional LED. The lower electron leakage current, higher hole injection efficiency, and consequently mitigated efficiency droop are achieved. The significant decrease of electrostatic field at the interface between the last barrier and the EBL of the LED could be one of the main reasons for these improvements.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1034004,50825603,and 51210011)the Fundamental Research Funds for the Central Universities,China(Grant No.12QX14)
文摘A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes (LEDs). The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional A1GaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.
基金supported by the National Natural Science Foundation of China(Grant No.51172079)the Science and Technology Program of Guangdong Province,China(Grant Nos.2010B090400456 and 2010A081002002)the Science and Technology Program of Guangzhou City,China(Grant No.11A52091257)
文摘InGaN/AIlnGaN superlattice (SL) is designed as the electron blocking layer (EBL) of an InGaN/GaN-based light- emitting diode (LED). The energy band structure, polarization field at the last-GaN-barrier/EBL interface, carrier concen- tration, radiative recombination rate, electron leakage, internal quantum efficiency (IQE), current-voltage (l-V) perfor- mance curve, light output-current (L-l) characteristic, and spontaneous emission spectrum are systematically numerically investigated using APSYS simulation software. It is found that the fabricated LED with InGaN/AIInGaN SL EBL exhibits higher light output power, low forward voltage, and low current leakage compared with those of its counterparts. Meanwhile, the efficiency droop can be effectively mitigated. These improvements are mainly attributed to the higher hole injection efficiency and better electron confinement when InGaN/AIlnGaN SL EBL is used.
文摘P-InGaN/p-GaN superlattices (SLs) are developed for a hole accumulation layer (HAL) of a blue light emitting diode (LED). Free hole concentration as high as 2.6× 1018 cm-3 is achieved by adjusting the Cp2Mg flow rate during the growth of p-InGaN/p-GaN SLs. The p-InGaN/p-GaN SLs with appropriate Cp2Mg flow rates are then incorporated between the multi-quantum well and A1GaN electron blocking layer as an HAL, which leads to the enhancement of light output power by 29% at 200 mA, compared with the traditional LED without such SL HAL. Meanwhile, the efficiency droop is also effectively alleviated in the LED with the SL HAL. The improved performance is attributed to the increased hole injection efficiency, and the reduced electron leakage by inserting the p-type SL HAL.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61176043)the Special Funds for Provincial Strategic and Emerging Industries Projects of Guangdong, China (Grant Nos. 2010A081002005, 2011A081301003, and 2012A080304016)
文摘The characteristics of a blue light-emitting diode (LED) with an AIlnN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carder concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AIInN/GaN SL EBL has better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region than the LED with a conventional rectangular AIGaN EBL or a A1GaN/GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.
基金Project supported by the National Natural Science Foundation of China (Grant No.61176043)the Special Funds for Provincial Strategic and Emerging Industries Projects of Guangdong,China (Grant Nos.2010A081002005,2011A081301003,and 2012A080304016)
文摘The efficiency enhancement of an InGaN light-emitting diode (LED) with an A1GaN/InGaN superlattice (SL) electron-blocking layer (EBL) is studied numerically, which involves the light-current performance curve, internal quan- tum efficiency electrostatic field band wavefunction, energy band diagram carrier concentration, electron current density, and radiative recombination rate. The simulation results indicate that the LED with an A1GaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular A1GaN EBL or a normal A1GaN/GaN SL EBL because of the appropriately modified energy band diagram, which is favorable ibr the injection of holes and confinement of elec- trons. Additionally, the efficiency droop of the LED with an AIGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.
基金Project supported by the National High Technology Program of China(Nos.2011AA03A105,2013AA03A101)the National Natural Science Foundation of China(Nos.61306051,61306050,11474105)+5 种基金the Beijing Municipal Science and Technology Project(No.D12110300140000)the National Basic Research Program of China(No.2011CB301902)the Industry-Academia-Research Union Special Fund of Guangdong Province of China(No.2012B091000169)the Science&Technology Innovation Platform of Industry-Academia Research Union of Guangdong Province-Ministry Cooperation Special Fund of China(No.2012B090600038)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20134407110008)the Science research innovation foundation of South China Normal University of China(No.2013kyjj041)
文摘The characteristics ofnitride-based blue light-emitting diodes (LEDs) with A1GaN composition-graded barriers are analyzed numerically. The carrier concentrations in the quantum wells (QWs), the energy band di- agrams, the electrostatic fields, and the light output power are investigated by APSYS software. The simulation results show that the LED with AlGaN composition-graded barriers has a better performance than its AlGaN/InGaN counterpart owing to the increase of hole injection and the enhancement of electron confinement. The simulation results also suggest that the output power is enhanced significantly and the efficiency droop is markedly improved when the AIGaN barriers are replaced by AlGaN composition-graded barriers.