Improvement of characteristics of InGaN light-emitting diode by using a staggered AlGaN electron-blocking layer

The optical and physical properties of InGaN light-emitting diode (LED) with a specific design of 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 of optical performance compared with the design of 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 LED could be one of the main reasons for these improvements.     

Improvement of characteristics of an InGaN light-emitting diode by using a staggered AlGaN electron-blocking layer

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.     

Modeling and simulation of efficiency droop in GaN-based blue light-emitting diodes incorporating the effect of reduced active volume of InGaN quantum wells

The efficiency droop of InGaN-based blue light-emitting diodes (LEDs) is analyzed using numerical simulations with a modified ABC carrier recombination model. The ABC model is modified to include the effect of reduced effective active volume of InGaN quantum wells (QWs) and incorporated into the numerical simulation program. It is found that the droop of internal quantum efficiency (IQE) can be well explained by the effect of reduced light-emitting active volume without assuming a large Auger recombination coefficient. A simulated IQE curve with the modified ABC model is found to fit quite well with a measured efficiency curve of an InGaN LED sample when the effective active volume takes only 2.5% of the physical volume of QWs. The proposed numerical simulation model incorporating the reduced effective active volume can be advantageous for use in the modeling and simulation of InGaN LEDs for higher efficiency.     

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AlGaN hole blocking layer

Blue InGaN light-emitting diodes (LEDs) with a conventional electron blocking layer (EBL), a common n-AlGaN hole blocking layer (HBL), and an n-AlGaN HBL with gradual Al 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-AlGaN HBL with gradual Al composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conventional p-AlGaN EBL or a common n-AlGaN HBL. Meanwhile, the efficiency droop is alleviated when an n-AlGaN HBL with gradual Al composition is used.     

Efficiency droop alleviation in blue light emitting diodes using the InGaN/GaN triangular-shaped quantum well

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.     

Enhanced carrier injection in InGaN/GaN multiple quantum wells LED with polarization-induced electron blocking barrier

In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In_0.1Ga_0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al_0.2Ga_0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.     

Performance enhancement of an InGaN light-emitting diode with an AlGaN/InGaN superlattice electron-blocking layer

The efficiency enhancement of an InGaN light-emitting diode(LED) with an AlGaN/InGaN superlattice(SL)electron-blocking layer(EBL) is studied numerically,which involves the light-current performance curve,internal quantum 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 AlGaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular AlGaN EBL or a normal AlGaN/GaN SL EBL because of the appropriately modified energy band diagram,which is favorable for the injection of holes and confinement of electrons.Additionally,the efficiency droop of the LED with an AlGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.     

The advantage of blue InGaN multiple quantum wells light-emitting diodes with p-AlInN electron blocking layer

InGaN based light-emitting diodes (LEDs) with different electron blocking layers have been numerically investigated using the APSYS simulation software. It is found that the structure with a p-AlInN electron blocking layer showes improved light output power, lower current leakage, and smaller efficiency droop. Based on numerical simulation and analysis, these improvements of the electrical and optical characteristics are mainly attributed to the efficient electron blocking in the InGaN/GaN multiple quantum wells (MQWs).     

具有三角形InGaN/GaN多量子阱的高内量子效率的蓝光LED(英文)

对InGaN量子阱LED的内量子效率进行了优化研究。分别对发光光谱、量子阱中的载流子浓度、能带分布、静电场和内量子效应进行了理论分析。对具有不同量子阱数量的InGaN/GaN LED进行了理论数值比对研究。研究结果表明,对于传统结构的LED而言,2个量子阱的结构相对于5个和7个量子阱具有更好的光学性能。同时还研究了具有三角形量子阱结构的LED,研究结果显示,三角形多量子阱结构具有较高的电致发光强度、更高的内量子效率和更好的发光效率,所有的优点都归因于较高的电子-空穴波函数重叠率和低的Stark效应所产生的较高的载流子输入效率和复合发光效率。     

Efficiency enhancement of an InGaN light-emitting diode with a p-AlGaN/GaN superlattice last quantum barrier

In this study,the efficiency droop of an InGaN light-emitting diode(LED)is reduced significantly by using a pAlGaN/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).     

新型电子阻挡层结构对蓝光InGaN发光二极管性能的提高

分别对3种不种电子阻挡层的蓝光AlGaN LED进行数值模拟研究。3种阻挡层结构分别为传统AlGaN电子阻挡层,AlGaN-GaN-AlGaN电子阻挡层和Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层。此外对这对三种器件的活性区的载流子浓度、能带图、静电场和内量子效率进行比较和分析。研究结果表明,相较于传统AlGaN和AlGaN-GaN-AlGaN两种电子阻挡层的LED,具有Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层结构的LED具有较高的空穴注入效率、较低的电子外溢现象和较小的静电场(活性区)。同时,具有Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层结构的LED的efficiency droop现象也得到一定的缓解。     

p-AlGaN电子阻挡层Al组分对Si衬底绿光LED性能影响的研究

在Si(111)衬底上利用MOCVD方法生长了具有不同Al组分p-AlGaN电子阻挡层的绿光InGaN/GaN LED结构,并对其光电性能进行了研究.结果表明,不同Al组分样品的量子效率随电流密度的变化规律呈现多样性.在很低电流密度范围,LED量子效率随Al组分升高而下降;在较高电流密度范围,LED量子效率随Al组分升高而升高,即此时缓解了量子效率随电流密度增大而衰退的速率(即droop效应);但随着电流密度的进一步升高,反而加快了量子效率衰退的速率.这些现象解释为不同Al组分的p-AlGaN对空穴和电子 关键词： 氮化镓 p-AlGaN 绿光LED 量子效率     

Investigation of blue InGaN light-emitting diodes with p-AlGaN/InGaN superlattice interlayer

The blue InGaN light-emitting diodes (LEDs), employing a lattice-compensated p-AlGaN/InGaN superlattice (SL) interlayer to link the last quantum barrier and electron blocking layer (EBL), are proposed and investigated numerically. The simulation results indicate that the newly designed LEDs have better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region over the conventional LEDs mainly attributed to the mitigated polarization-induced downward band bending. Furthermore, the markedly improved output power and efficiency droop are also suggested when the conventional LEDs corresponding to experiment data are replaced by the newly designed LEDs.     

Performance enhancement of InGaN light-emitting diodes with a leakage electron recombination quantum well

An InGaN light-emitting diodes with a leakage electron recombination (LER) quantum well have been proposed and investigated numerically by using the APSYS simulation software. The simulation results indicate that the AlGaN electron blocking layer inserted between the last two quantum wells changed the carrier concentrations distribution, and the leakage electrons can be further recombined with holes in the LER quantum well which can decrease the electrons that spill out from active region. As a result, the internal quantum efficiency and light output power are markedly improved attributed to LER quantum well.     

Effect of localized states on internal quantum efficiency of III‐nitride LEDs

A model is suggested accounting for effects of localized electron and hole states formed by composition fluctuations in the InGaN active region of a III‐nitride LED on non‐radiative carrier recombination at threading dislocations. The model enables explanation of the abnormal temperature dependence of internal quantum efficiency (IQE) of a green LED structure recently observed at low current densities. The theoretical predictions are in quantitative agreement with experiment in the temperature range between 200 K and 453 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of nitride-based dual-wavelength light- emitting diodes with an InAlN electron-blocking layer and with p-type doped barriers

The advantages of nitride-based dual-wavelength light-emitting diodes (LEDs) with an InAlN electron blocking layer (EBL) are studied. The emission spectra,carrier concentration in the quantum wells (QWs),energy band and internal quantum efficiency (IQE) are investigated. The simulation results indicate that an LED with an InAlN EBL performs better over a conventional LED with an AlGaN EBL and an LED with p-type-doped QW barriers. All of the advantages are due to the enhancement of carrier confinement and the lower electron leakage current. The simulation results also show that the efficiency droop is markedly improved and the luminous intensity is greatly enhanced when an InAlN EBL is used.     

Improved performance of InGaN light-emitting diodes with a novel sawtooth-shaped electron blocking layer

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.     

It's not easy being green: Strategies for all‐nitrides,all‐colour solid state lighting

The design strategy presently employed to obtain ‘white’ light from semiconductors combines the emission of an InGaN blue or UV light‐emitting diode (LED) with that of one or more yellow‐orange phosphors. While commercially successful, this approach achieves good colour rendering only by increasing the number and spectral range of the phosphors used; compared to the alternative of combining ‘true’ red, green and blue (RGB) sources, it is intrinsically inefficient. The two major roadblocks to the RGB approach are 1. the green gap in the internal quantum efficiency (IQE) of LEDs; 2. the diode droop in the efficiency of LEDs at higher current densities. The physical origin of these effects, in the case of III‐nitrides, is generally thought to be a combination of Quantum Confined Stark Effect (QCSE) and Auger Effect (AE). These effects respectively reduce the electron–hole wave‐ function overlap of In‐rich InGaN quantum wells (QW), and provide a non‐radiative shunt for electron–hole recombination, particularly at higher excitation densities. SORBET, a novel band gap engineering strategy based upon quantum well intermixing (QWIM), offers solutions to both of the roadblocks mentioned above. In this introduction to SORBET, its great potential is tested and confirmed by the results of simulations of green InGaN diodes performed using the TiberCAD device modelling suite, which calculates the macroscopic properties of real‐world optoelectronic and electronic devices in a multiscale formalism. An alternative approach to the realisation of RGB GaN‐based LEDs through doping of an active layer by rare earth (RE) ions will also be briefly described. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

量子阱数量变化对InGaN/AlGaN LED的影响

采用软件理论分析的方法分析了InGaN/AlGaN量子阱数量变化对发光二极管内量子效率、电子空穴浓度分布、载流子溢出产生的影响。分析结果表明:量子阱的个数不是越多越好,LED的光学性质和量子阱的个数并不成线性关系。量子阱个数太少时,电流溢出现象较明显;而当量子阱个数太多时,极化现象明显,且会造成材料浪费。因此应根据工作电流选择合适的量子阱个数。     

Improvement of the carrier distribution with GaN/InGa N/AlGaN/InGaN/GaN composition-graded barrier for InGaN-based blue light-emitting diode

In Ga N light-emitting diodes(LEDs) with Ga N/In Ga N/Al Ga N/In Ga N/Ga N composition-graded barriers are proposed to replace the sixth and the middle five Ga N barriers under the condition of removing the electron blocking layer(EBL)and studied numerically in this paper. Simulation results show that the specially designed barrier in the sixth barrier is able to modulate the distributions of the holes and electrons in quantum well which is adjacent to the specially designed barrier. Concretely speaking, the new barrier could enhance both the electron and hole concentration remarkably in the previous well and reduce the hole concentration for the latter one to some extent along the growth direction. What is more,a phenomenon, i.e., a better carrier distribution in all the wells, just appears with the adoption of the new barriers in the middle five barriers, resulting in a much higher light output power and a lower efficiency droop than those in a conventional LED structure.