InGaN/GaN超晶格厚度对Si衬底GaN基蓝光发光二极管光电性能的影响

采用有机金属化学气相沉积技术在Si(111)衬底上生长蓝光多量子阱发光二极管(LED) 结构, 通过在量子阱下方分别插入两组不同厚度的InGaN/GaN超晶格, 比较了超晶格厚度对LED光电性能的影响. 结果显示: 随超晶格厚度增加, 样品的反向漏电流加剧; 300 K下电致发光仪测得随着电流增加, LED发光光谱峰值的蓝移量随超晶格厚度增加而减少, 但不同超晶格厚度的两个样品在300 K下的电致发光强度几乎无差异. 结合高分辨X射线衍射仪、扫描电子显微镜、透射电子显微镜对样品的位错密度和V形坑特征分析, 明确了两样品反向漏电流产生巨大差异的原因是由于超晶格厚度大的样品具有更大的V形坑和V形坑密度, 而V形坑可作为载流子的优先通道, 使超晶格更厚的样品反向漏电流加剧. 通过对样品非对称(105)面附近的X射线衍射倒易空间图分析, 算得超晶格厚度大的样品其InGaN量子阱在GaN上的弛豫度也大, 即超晶格厚度增加有利于减小InGaN量子阱所受的应力. 综合以上影响LED发光效率的消长因素, 导致两样品最终的发光强度相近.     

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。     

影响GaN基蓝光LED能带结构与光谱特性关系的仿真研究

本文采用Silvaco TCAD软件对GaN基InGaN/GaN量子阱蓝光发光二极管(LED)的光谱特性进行了仿真研究。研究结果表明:光谱会随着注入电压的增加而产生蓝移现象,并出现0.365μm处的紫外光发光峰;发光效率在正向电流较小时增长很快,随着正向电流进一步增加而逐渐趋于饱和;随着量子阱中In组分和量子阱阱层厚度的增加,发光光谱出现红移现象,并且发光效率下降。仿真结果对GaN基InGaN/GaN量子阱结构蓝光LED的设计和优化提供一定的依据。     

硅衬底InGaN/GaN基蓝光发光二极管droop效应的研究

InGaN/GaN基阱垒结构LED当注入的电流密度较大时, LED的量子效率随注入电流密度增大而下降, 即droop效应.本文在Si (111)衬底上生长了 InGaN/GaN 基蓝光多量子阱结构的LED,通过将实验测量的光电性能曲线与利用ABC模型模拟的结果进行对比, 探讨了droop效应的成因.结果显示:温度下降会阻碍电流扩展和降低空穴浓度, 电子在阱中分布会越来越不平衡,阱中局部区域中因填充了势能越来越高的电子而溢出阱外, 从而使droop效应随着温度的降低在更小的电流密度下出现且更为严重, 不同温度下实验值与俄歇复合模型模拟的结果在高注入时趋势相反.这此结果表明,引起 droop效应的主因不是俄歇非辐射复合而是电子溢出,电子溢出的本质原因是载流子在阱中分布不均衡.     

GaN基纳米阵列LED器件制备及发光特性

为了降低GaN材料中因应变诱导的量子斯托克斯效应,增加器件有源区内的电子-空穴波函数在实空间的交叠从而提高GaN基LEDs的发光效率,采用紫外软压印技术制备了均匀的周期性纳米柱阵列结构,结合常规LED器件微加工技术获得了In GaN/GaN基蓝光与绿光纳米阵列LED器件并对其进行了表征分析。结果表明:纳米柱阵列LED器件具有均匀的发光和稳定的光电性能。纳米结构不仅有效缓解了量子阱中的应力积累(弛豫度~70%),提高了器件的辐射复合几率和出光效率,同时结合纳米柱侧壁的化学钝化处理进一步降低了器件有源区的缺陷密度,显著降低了LED器件的漏电流(~10-7),最终提高了器件的发光效率。     

蓝光激光器结构中InGaN/GaN多量子阱界面效应的精细光致发光光谱研究

金属有机化学气相沉积(MOCVD)方法制备InGaN/GaN多量子阱结构时,在GaN势垒层生长的N2载气中引入适量H2,能够有效改善阱/垒界面质量从而提升发光效率.本工作利用光致发光(PL)光谱技术,对蓝光激光器结构中的InGaN/GaN多量子阱的发光性能进行了精细的光谱学测量与表征,研究了通H2生长对量子阱界面的调控...     

中高温GaN插入层厚度对蓝光LED光电性能的影响

利用金属有机气相化学沉积(MOCVD)技术在蓝宝石图形衬底上生长GaN基蓝光LED,并系统研究了不同中高温GaN插入层厚度对其光电性能的影响。利用芯片测试仪和原子力显微镜(AFM)表征了GaN基蓝光LED外延片的光电性能以及表面形貌。当中高温GaN插入层厚度从60 nm增加至100 nm时,V形坑尺寸从70~110 nm增加至110~150 nm。当注入电流为20 mA时,LED芯片的光功率从21.9 mW增加至24.1mW;当注入电流为120 mA时,LED芯片的光功率从72.4 mW增加至82.4 mW。对V形坑尺寸调控LED光电性能的相关物理机制进行了分析,结果表明:增大V形坑尺寸有利于增加空穴注入面积和注入效率,进而提高LED器件的光功率。     

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     

类金字塔状GaN微米锥的形貌及发光性能

三维结构GaN基LED能够解决二维GaN基薄膜LED中存在的量子限制斯塔克效应、效率骤降、发光波长单一等问题。基于此,本文对三维类金字塔状GaN微米锥的发光性能进行了详细的研究。通过金属有机化合物化学气相沉积原位沉积SiN_x掩模层后,首先制备了底面尺寸为8μm、高度7.5μm的类金字塔状GaN微米锥,之后在其半极性面外延生长了3个周期的InGaN/GaN多量子阱。通过阴极荧光测试发现,类金字塔状GaN微米锥的半极性面上不同位置发光波长不同;变功率微区光致发光测试表明,类金字塔状GaN微米锥的半极性面在InGaN/GaN多量子阱沉积之后极化场较弱;对InGaN/GaN多量子阱进行了透射电镜表征,结合阴极荧光光谱的结果最终解释了In原子在类金字塔状GaN微米锥上的迁移机理。利用其半极性面不同位置发光波长不同的结构特点及光学特性,可以制备多波长发射LED。     

InxGa1-xN量子阱蓝光LED光电特性与量子阱束缚态能级的关系

运用软件模拟和理论计算的方法分析了量子阱宽度的变化对量子阱束缚态能级与光电性能产生的影响,建立了束缚态分裂能级理论模型。分析结果表明:当量子阱宽较窄时,极化效应导致的能带弯曲是光谱红移的主要原因,而电子泄漏是导致效率下降的主要原因;当阱宽较大时,能级填充是导致光谱红移的主要原因,俄歇复合与载流子离域是导致效率下降的主要原因。由本文得出,当量子阱宽为2.5～3.5 nm时,InGaN/GaN发光二极管获得最大内量子效率与发光效率。     

A dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

A strain-compensated InGaN quantum well(QW) active region employing a tensile AlGaN barrier is analyzed.Its spectral stability and efficiency droop for a dual-blue light-emitting diode(LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LEDs based on a stacking structure of two In0.18Ga0.82N/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate.It is found that the optimal performance is achieved when the Al composition of the strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW.The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW,which can provide a better carrier confinement and effectively reduce leakage current.     

Dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

Strain-compensated InGaN quantum well (QW) active region employing tensile AlGaN barrier is analyzed. Its spectral stability and efficiency droop for dual-blue light-emitting diode (LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LED based on stacking structure of two In_0.18Ga_0.82N/GaN QWs and two In_0.12Ga_0.88N/GaN QWs on the same sapphire substrate. It is found that the optimal performance is achieved when the Al composition of strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW. The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW that can provide a better carrier confinement and effectively reduce leakage current.     

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.     

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).     

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.     

Investigation of wavelength-dependent efficiency droop in InGaN light-emitting diodes

The physical mechanisms leading to the efficiency droop of InGaN/GaN light-emitting diodes (LEDs) are theoretically investigated. We first discuss the effect of Auger recombination loss on efficiency droop by taking different Auger coefficients into account. It is found that the Auger recombination process plays a significant nonradiative part for carriers at typical LED operation currents when the Auger coefficient is on the order of 10⁻³⁰ cm⁶ s⁻¹. Furthermore, the InGaN/GaN multiple-quantum-well (MQW) LEDs with varied indium compositions in InGaN quantum wells are studied to analyze the wavelength-dependent efficiency droop. The simulation results show that the wavelength-dependent efficiency droop is caused by several different effects including non-uniform carrier distribution, electron overflow, built-in electrostatic field induced by spontaneous and piezoelectric polarization, and Auger recombination loss. These internal physical mechanisms are the critical factors resulting in the wavelength-dependent efficiency droop in InGaN/GaN MQW LEDs.     

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。     

Improved carrier injection and confinement in InGaN light-emitting diodes containing GaN/AlGaN/GaN triangular barriers

In this study, an InGaN lighting-emitting diode(LED) containing GaN/AlGaN/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 AlGaN 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.     

Performance improvement of blue light-emitting diodes with an AlInN/GaN superlattice electron-blocking layer

The characteristics of a blue light-emitting diode (LED) with an AlInN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AlInN/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 AlGaN EBL or a AlGaN/ GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.