表面InGaN厚度对GaN基发光二极管特性的影响

通过调整GaN基发光二极管(LED)表面InGaN层的厚度,发现在20 mA电流驱动下,LED器件的正向压降有明显差距.本文考虑了极化效应的影响,通过求解InGaN/GaN三角形势阱内二维空穴气浓度以及空穴隧穿概率的变化,求得了表面InGaN层厚度不同时器件正向压降的变化趋势,发现理论结果与实验结果有很好的吻合.同时得到了获得最低正向压降的表面InGaN厚度. 关键词： 极化 二维空穴气 隧穿概率     

高效InGaN/AlInGaN发光二极管的结构设计及其理论研究（英文）

利用Advanced Physical Models of Semiconductor Devices(APSYS)理论对比研究了InGaN/AlInGaN和InGaN/GaN多量子阱作为有源层的InGaN基发光二极管的结构和电学特性。与InGaN/GaN基LED中GaN作为垒层材料相比,在AlInGaN材料体系中,通过调节AlInGaN中Al和In的组分可以优化器件的性能。当InGaN阱层材料中In组分为8%时,可以实现无应力的In0.08Ga0.92N/AlInGaN基LED。在这种无应力结构中可以进一步降低大功率LED的"效率下降"(Effciency droop)问题。理论模拟结果显示,四元系AlInGaN作为垒层可以进一步减少载流子泄露,增加空穴注入效率,减少极化场对器件性能的影响。在In0.08Ga0.92N/AlInGaN量子阱中的载流子浓度、有源层的辐射复合率、电流特性曲线和内量子效率等方面都优于InGaN/GaN基LED。无应变AlInGaN垒层代替传统的GaN垒层后,能够得到高效的发光二极管,并且大电流注入下的"效率滚降"问题得到改善。     

高效InGaN/AlInGaN发光二极管的结构设计及其理论研究

利用Advanced Physical Models of Semiconductor Devices (APSYS)理论对比研究了InGaN/AlInGaN 和 InGaN/GaN多量子阱作为有源层的InGaN基发光二极管的结构和电学特性。与InGaN/GaN 基LED 中GaN作为垒层材料相比,在AlInGaN材料体系中,通过调节AlInGaN中Al和In的组分可以优化器件的性能。当InGaN阱层材料中In组分为8%时,可以实现无应力的In_0.08Ga_0.92N/AlInGaN基 LED。在这种无应力结构中可以进一步降低大功率LED的"效率下降"(Effciency droop)问题。理论模拟结果显示,四元系AlInGaN作为垒层可以进一步减少载流子泄露,增加空穴注入效率,减少极化场对器件性能的影响。在In_0.08Ga_0.92N /AlInGaN量子阱中的载流子浓度、有源层的辐射复合率、电流特性曲线和内量子效率等方面都优于InGaN/GaN基LED。无应变AlInGaN垒层代替传统的GaN垒层后,能够得到高效的发光二极管,并且大电流注入下的"效率滚降"问题得到改善。     

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。     

GaN基蓝光发光二极管的波长稳定性研究

尽管GaN基蓝绿光发光二极管（LED）已进入大规模商品化阶段，但其发光波长随注入电流的变化仍是一个尚未解决的关键技术难题.同时，蓝绿光LED电注入发光光谱的半高全宽多为25nm以上.通过优化LED器件材料的生长条件和总应变量，获得了高质量的InGaN/GaN多量子阱LED外延片.由此制作的LED器件在0—120?mA的注入电流下，发光波长变化小于1nm.在20mA的正向电流下，其光谱半高全宽只有18nm，且随注入电流变化较小. 关键词： GaN 发光二极管 波长稳定性     

引入n型InGaN/GaN超晶格层提高量子阱特性研究

利用金属有机物化学气相淀积技术在蓝宝石衬底上生长了InGaN/GaN量子阱结构. 研究了引入n型InGaN薄层或InGaN/GaN超晶格层的量子阱特性,结果表明通过引入n型InGaN薄层或InGaN/GaN超晶格层缓解了量子阱有源区中的应力,改善了多量子阱表面形貌,减少了V型缺陷密度,而且提高了多量子阱的光致发光强度,从而也改进了LED的发光效率. 关键词： InGaN/GaN多量子阱 原子力显微镜 X射线双晶衍射 光致发光     

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     

V形坑尺寸对硅衬底InGaN/AlGaN近紫外LED光电性能的影响

使用MOCVD在图形化Si衬底上生长了InGaN/AlGaN近紫外LED,通过改变低温GaN插入层的厚度调控V形坑尺寸,系统地研究了V形坑尺寸对InGaN/AlGaN近紫外LED(395 nm)光电性能的影响。结果表明,低温GaN插入层促进了V形坑的形成,并且V形坑尺寸随着插入层厚度的增加而增大。在电学性能方面,随着V形坑尺寸的增大,-5 V下的漏电流从5.2×10~(-4)μA增加至6.5×10~2μA;350 mA下正向电压先从3.55 V降至3.44 V,然后升高至3.60 V。在光学性能方面,随着V形坑尺寸的增大,35 A/cm~2下的归一化外量子效率先从0.07提高至最大值1,然后衰退至0.53。对V形坑尺寸影响InGaN/AlGaN近紫外LED光电性能的物理机理进行了分析,结果表明:InGaN/AlGaN近紫外LED的光电性能与V形坑尺寸密切相关,最佳的V形坑尺寸为120~190 nm,尺寸太大或者太小都会降低器件性能。     

GaN基多量子阱蓝光LED的γ辐照效应

本文用4×104Ci(1Ci=3.7×1010Bq)的60Co源(剂量率2×105rad(Si)/h)对GaN基InGaN/GaN多量子阱蓝光LED进行5种剂量的γ射线的辐照实验.通过辐照前后蓝光LED的波长、色纯度、最大半峰宽(FWHM)和电流-电压(I-V)、电流-光通量(I-F)等电光学特性分析,得到γ射线对GaN基LED器件的辐照效应.结果发现,辐照后LED器件的发光一致性和均匀性变差,在20mA工作电流下,最大剂量下器件发光强度衰减近90%,光通量衰减约40%,并得到器件的抗辐照能力的参数τ0Kγ为4.039×10-7rad.s-1,发现较低的正向偏压下(小于2.6V)器件的饱和电流随辐照总剂量增大而增大.     

大功率GaN基发光二极管的电流扩展效应及电极结构优化研究

定性分析了GaN基LED的电流扩展效应，发现电流密度和电流横向扩展的有效长度对电流均匀扩展有很大影响.基于此，对GaN基大功率LED提出了优化的电极结构，以减缓电流拥挤效应，降低器件串联电阻.通过用红外热像仪测量器件表面的温度分布，发现具有优化的环形插指电极结构的GaN基大功率LED表面温度分布比较均匀，证明芯片接触处电流扩展均匀，局部电流密度降低，减小了焦耳热的产生，增强了器件的可靠性.     

Recent progress in single chip white light-emitting diodes with the InGaN underlying layer

Tremendous progress has been achieved in white light-emitting diodes (LEDs). To further improve the quality of white light and simplify the fabrication process, a single chip white-light LED with the InGaN underlying layer (UL) was studied and fabricated. The turn-on voltage of this type of LED was 2.7 V, and the spectrum at a forward bias current of 20 mA was comprised of blue (443 nm) and yellow (563 nm) lights. The intensity ratio of blue to yellow light was almost constant with the in- creasing injectio...     

High power and high reliability GaN/InGaN flip-chip light-emitting diodes

High-power and high-reliability GaN/InGaN flip-chip light-emitting diodes (FCLEDs) have been demonstrated by employing a flip-chip design, and its fabrication process is developed. FCLED is composed of a LED die and a submount which is integrated with circuits to protect the LED from electrostatic discharge (ESD) damage. The LED die is flip-chip soldered to the submount, and light is extracted through the transparent sapphire substrate instead of an absorbing Ni/Au contact layer as in conventional GaN/InGaN LED epitaxial designs. The optical and electrical characteristics of the FCLED are presented. According to ESD IEC61000-4-2 standard (human body model), the FCLEDs tolerated at least 10\,kV ESD shock have ten times more capacity than conventional GaN/InGaN LEDs. It is shown that the light output from the FCLEDs at forward current 350mA with a forward voltage of 3.3\,V is 144.68\,mW, and 236.59\,mW at 1.0\,A of forward current. With employing an optimized contact scheme the FCLEDs can easily operate up to 1.0\,A without significant power degradation or failure. The life test of FCLEDs is performed at forward current of 200\,mA at room temperature. The degradation of the light output power is no more than 9\% after 1010.75\,h of life test, indicating the excellent reliability. FCLEDs can be used in practice where high power and high reliability are necessary, and allow designs with a reduced number of LEDs.     

InGaN/GaN MQD p–n junction photodiodes

The p–n junction photodiodes with InGaN/GaN MQD have been prepared by metal-organic chemical vapor deposition (MOCVD) growth; we achieved nanoscale InGaN self-assembled QDs in the well layers of the active region. The RT PL spectrum peak position for the fabricated InGaN/GaN MQD p–n Junction PDs is located at 464.6 nm and FWHM is 24.2 nm. After finishing device process, it was fond that the turn on voltage in forward bias and the break down voltage in reverse bias are about 3 and −13.5 V, respectively. Furthermore, with 1, 2, and 3 V applied bias, the maximum responsivity of the fabricated MQD p–n junction PD was observed at 350 nm, and the minimum of spectral response was measured at 465 nm. It was also found that the responsivity was nearly a constant from 390 to 440 nm. It seems to suggest that the spectral response in the range of 390–440 nm is due to the effect of the InGaN dots-in a-well active layers.     

Enhanced performance of InGaN light-emitting diodes with InGaN and composition-graded InGaN interlayers

The effects of InGaN light-emitting diodes (LEDs) with InGaN and composition-graded InGaN interlayers in the space of multiple quantum wells and electron blocking layer are studied numerically. The electrostatic field, energy band diagrams, carrier concentrations, light–current–voltage performances, and internal quantum efficiency (IQE) are investigated. Simulation results show that the light output power and IQE are both largely improved over the conventional LED structure due to the improvement in hole injection efficiency and electron blocking capability, especially for the LED with composition-graded InGaN interlayer.     

Enhancement of light-emission efficiency of ultraviolet InGaN/GaN multiple quantum well light emitting diode with InGaN underlying layer

Two ultraviolet InGaN/GaN light emitting diodes (LEDs) with and without InGaN underlying layer beneath the multiple quantum wells (MQWs) were grown by metal-organic vapor phase epitaxy. Based on the photoluminescence excitation measurements, it was found that the Stokes shift of the sample with a 10-nm-thick In_0.1Ga_0.9N underlying layer was about 64 meV, which was smaller than that of the reference sample without InGaN underlying layer, indicating a reduced quantum-confined Stark effect (QCSE) due to the decrease of the piezoelectric polarization field in the MQWs. In addition, by fitting the photon energy dependence of carrier lifetime values, the radiative recombination lifetime of the sample with and without InGaN underlying layer were obtained about 1.22 and 1.58 ns at 10?K, respectively. The shorter carrier lifetime also confirmed that the QCSE in the MQWs was weakened after inserting the InGaN underlying layer. In addition, although the depth of carrier localization in the sample with InGaN underlying layer became smaller, the nonradiative recombination centers (NRCs) inside it decreased, and thus suppressed the nonradiative recombination process significantly according to the electroluminescence measurement results. Compared to the reference sample, the efficiency droop behavior was delayed in the sample with InGaN underlying layer and the droop effect was also effectively alleviated. Therefore, the enhanced light-emission efficiency of ultraviolet InGaN/GaN MQW LEDs could be attributed to the decrease of QCSE and NRCs.     

Two dimensional electron gas in a hybrid GaN/InGaN/ZnO heterostructure with ultrathin InGaN channel layer

We investigated the influence of an ultrathin InGaN channel layer on two-dimensional electron gas (2DEG) properties in a newly proposed hybrid GaN/In_xGa_1−xN/ZnO heterostructure using numerical methods. We found that 2DEG carriers were confined at InGaN/ZnO and GaN/InGaN interfaces. Our calculations show that the probability densities of 2DEG carriers at these interfaces are highly influenced by the In mole fraction of the InGaN channel layer. Therefore, 2DEG carrier confinement can be adjustable by using the In mole fraction of the InGaN channel layer. The influence of an ultrathin InGaN channel layer on 2DEG carrier mobility is also discussed. Usage of an ultrathin InGaN channel layer with a low indium mole fraction in these heterostructures can help to reduce the short-channel effects by improvements such as providing 2DEG with higher sheet carrier density which is close to the surface and has better carrier confinement.     

硅衬底GaN蓝色发光材料转移前后应力变化研究

利用外延片压焊和湿法腐蚀技术将硅衬底上生长的InGaN多量子阱发光二极管(LED)薄膜材料转移到了新衬底上. 研究结果表明, 转移后的LED薄膜中GaN层受到的张应力变小,InGaN层受的压应力变大. 去除转移后LED薄膜中过渡层后,GaN层受到的张应力变大,而铟镓氮层受到的压应力基本不变. 将转移后的薄膜做成垂直结构的LED芯片后,其光电性能明显改善. 关键词： GaN 发光二极管 硅衬底 应力