选择性p型量子阱垒层掺杂在双波长发光二极管光谱调控中的作用

采用软件理论分析的方法对选择性p型掺杂量子阱垒层在InGaN双波长发光 二极管(LED)中的光谱调控作用进行模拟分析.分析结果表明, 选择性p型掺杂对量子阱中电子和空穴浓度分布的均衡性起到一定的调控作用, 在适当选择p型掺杂量子阱垒层层数的条件下,能够改善量子阱中载流子的 辐射复合速率, 降低溢出电子浓度,从而有效提高芯片内量子效率,并减缓内量子效率随驱动 电流增大而快速下降的趋势.随着活性层量子阱增加到特定数量, 选择性p型掺杂的调控效果更加明显, LED芯片的双波长发光峰强度达到基本均衡.     

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.     

渐变型量子阱垒层厚度对GaN基双波长发光二极管发光特性调控的研究

采用软件理论分析的方法对渐变型量子阱垒层厚度的InGaN双波长发光二极(LED)的载流子浓度分布、 能带结构、自发发射谱、内量子效率、发光功率及溢出电子流等进行研究.分析结果表明, 增大量子阱垒层厚度会影响空穴在各量子阱的注入情况, 对双波长LED各量子阱中空穴浓度分布的 均衡性及双波长发光光谱的调控起到一定作用,但会导致内量子效率严重下降; 而当以特定的方式从n电极到p电极方向递减渐变量子阱垒层厚度时, 活性层量子阱的溢出电子流 得到有效的控制, 双发光峰强度达到基本一致, 同时芯片的内量子效率下降得到了有效控制, 且具备大驱动电流下较好的发光特性.     

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。     

含有量子点的双波长LED的光谱调控

本文通过对含有高In组分量子点的双波长LED进行了模拟计算, 并对器件的能带结构、载流子浓度、复合速率和辐射光谱进行了研究. 通过对器件结构的调整与对比, 发现蓝绿双波长LED的绿光量子阱中加入高In组分量子点后可以拓宽辐射光谱, 使LED光谱具有更高的显色指数, 为实现无荧光粉的白光LED提供指导. 量子点对载流子具有很强的束缚能力, 并且载流子在量子点处具有更短的寿命, 载流子优先在量子点处复合, 量子点处所对应的黄光与量子阱润湿层所对应的绿光的比例随量子点浓度的增大而增大, 载流子浓度较低时以量子点处的黄光辐射为主, 载流子浓度变大后, 量子点复合逐渐达到饱和, 绿光辐射开始占据主导. 对间隔层厚度和间隔层掺杂浓度的调节可以很方便地调控载流子的分布, 从而实现对含有量子点的双波长LED两个活性层辐射速率的调控. 结果表明, 通过对量子点浓度、间隔层厚度、间隔层掺杂浓度的控节可以很好地实现对LED辐射光谱的调控作用. 关键词： GaN 量子点 光谱调控 双波长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.     

不同掺杂类型的GaN间隔层和量子阱垒层对双波长LED作用的研究

采用软件理论分析的方法对不同掺杂类型的GaN间隔层和量子阱垒层在InGaN/GaN多量子阱双波长发光二极管中对发光光强、内量子效率、电子空穴浓度分布、溢出电流等作用进行模拟分析. 分析结果表明,p型掺杂的GaN间隔层与量子阱垒层的引入同不掺杂和n型掺杂两种类型比较,可以大大减少溢出电子流,极大地提高各量子阱内空穴浓度,提高双波长发光二极管的发光强度,极大的改善内量子效率随电流增大而下降问题. 关键词： GaN 掺杂类型 数值模拟 双波长发光二极管     

Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers

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.     

Effects of Mg doping in the quantum barriers on the efficiency droop of GaN based light emitting diodes

The effects of Mg doping in the quantum barriers(QBs) on the efficiency droop of GaN based light emitting diodes(LEDs) were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells(QWs), both may reduce the efficiency droop. However,heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop.     

Efficiency droop suppression in GaN-based light-emitting diodes by chirped multiple quantum well structure at high current injection

Gallium nitride(Ga N) 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 m A/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.     

Influence of electron-beam irradiation in SEM on the cathodoluminescence and electron-beam-induced current in InGaN/GaN light-emitting diodes with a buried active region

The influence of irradiation in a scanning electron microscope on the optical properties inherent to light-emitting diodes (LEDs) with multiple InGaN/GaN quantum wells, assembled by means of the flip-chip mounting technique, has been investigated via the cathodoluminescence (CL) and electron-beam-induced current methods. It is demonstrated that the action of an electron beam qualitatively varies both these LEDs and structures with a thin upper GaN layer only at large beam energies. It has been revealed that irradiation not only leads to changes in the spectrum and intensity of CL but also decreases the energy corresponding to the excitation of emission associated with quantum wells. A similar effect is also observed in structures whose external quantum efficiency has been decreased several times due to long-running tests performed at an injection current density of 35 A/cm² and a temperature of 100°C.     

Investigation of InGaN green light-emitting diodes with chirped multiple quantum well structures

The effect of using chirped multiple quantum-well (MQW) structures in InGaN green light-emitting diodes (LEDs) is numerically investigated. An active structure, which is with both thick QWs with low indium composition on the p-side and thin QWs with high indium composition next to the n-region, is presented in this study. The thickness and indium composition in each single QW is specifically tuned to emit the same green emission spectrum. Comparing with conventional active structure design of green LEDs, which is using uniform MQWs, the output power is increased by 27% at 20 mA, and by 15% at 100 mA current injections. This improvement is mainly attributed to the enhanced efficiency of carrier injection into QWs and the improved capability of carrier transport.     

Improvement of green InGaN-based LEDs efficiency using a novel quantum well structure

The green light emitting diodes(LEDs)have lower quantum efficiency than LEDs with other emission wavelengths in the visible spectrum.In this research,a novel quantum well structure was designed to improve the electroluminescence(EL)of green InGaN-based LEDs.Compared with the conventional quantum well structure,the novel structure LED gained 2.14times light out power(LOP)at 20-mA current injection,narrower FWHM and lower blue-shift at different current injection conditions.     

Enhanced performance of GaN-based light-emitting diodes with InGaN/GaN superlattice barriers

GaN-based multiple quantum well light-emitting diodes （LEDs） with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.     

Enhancement of surface emission in deep ultraviolet AlGaN-based light emitting diodes with staggered quantum wells

The optical polarization properties of staggered AlGaN-AlGaN/AlN quantum wells (QWs) are investigated using the theoretical model based on the k·p method. The numerical results show that the energy level order and coupling relation of the valence subband structure change in the staggered QWs and the trend is beneficial to TE polarized transition compared to that of conventional AlGaN/AlN QWs. As a result, the staggered QWs have much stronger TE-polarized emission than conventional AlGaN-based QWs, which can enhance the surface emission of deep ultraviolet (DUV) light-emitting diodes (LEDs). The polarization control by using staggered QWs can be applied in high efficiency DUV AlGaN-based LEDs.     

In组分渐变提高InGaN/GaN多量子阱发光二极管发光性能

利用金属有机物化学气相沉积系统在蓝宝石衬底上通过有源层的变温生长,得到In组分渐变的量子阱结构,从而获得具有三角形能带结构的InGaN/GaN多量子阱发光二极管(LED)(简称三角形量子阱结构LED).变温光致发光谱结果表明,相对于传统具有方形能带结构的量子阱LED(简称方形量子阱结构LED),三角形量子阱结构有效提高了量子阱中电子和空穴波函数的空间交叠,从而增加了LED的内量子效率;电致发光谱结果表明,三角形量子阱结构LED器件与传统结构LED器件相比,明显改善了发光峰值波长随着电流的蓝移现象.通过以上     

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.     

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.     

Effect of Barrier Temperature on Photoelectric Properties of Ga N-Based Yellow LEDs

The effect of growth temperature of barriers on photoelectric properties of Ga N-based yellow light emitting diodes(LEDs) is investigated. It is found that as the barrier temperature increases, the crystal quality of multiquantum wells(MQWs) and the quality of well/barrier interface are improved, and the quantum well is thermally annealed, so that the indium atoms in the quantum well migrate to the equilibrium position, reducing the phase separation of the quantum well and improving the crystal quality of quantum wells(QWs). However, the external quantum efficiency(EQE) of the samples begins to decrease when raising the barrier temperature even further.One explanation may be that the higher barrier temperature destroys the local state in the quantum well and reduces the well/barrier interface quality. Therefore, a suitable barrier temperature is proposed, contributing to the improvement of the luminous efficiency of the yellow LEDs.     

非等温模型下LED芯片性能与衬底的关系

发光二极管(LED)中载流子的输运及复合决定了其非均匀的内热源强度及分布,而芯片温度又影响载流子的输运及复合,两者具有强烈的耦合关系。本文利用非等温多物理场耦合模型对以蓝宝石、Si及SiC为衬底的 LED芯片的内量子效率、光谱特性及光电转换效率进行了系统研究。结果表明:以SiC为衬底的LED芯片具有最小的效率下垂效应(Efficiency droop)及最高的光谱强度和光电转换效率。这是因为与其他两种衬底的LED芯片相比,以SiC为衬底的LED芯片具有最好的散热性能,因此非均匀温度场对其载流子输运及复合的影响最小,使得活性区中的载流子浓度显著增强,漏电流明显下降。