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     

关于InGaN/GaN多量子阱结构内量子效率的研究

利用金属有机物化学气相沉积技术在蓝宝石衬底(0001)面生长了InGaN/GaN多量子阱结构,并测量了其荧光(PL)光谱的峰位能量和发光效率对温度和注入载流子密度的依赖性.结果显示,该样品PL的峰位能量对温度的依赖性是"S形"的(降低-增加-降低),并且最大发光效率出现在50 K左右.前者反映了InGaN阱层中势能的非均一性和载流子复合的局域特征,后者则表明了将极低温度下的内量子效率设定为100%的传统界定方法应当被修正.进一步的研究结果显示,发光效率不仅是温度的函数,同时也是注入载流子密度的函数.为此我们对传统的基于PL光谱测量来确定某结构(或器件)内量子效率的方法进行了修正:在不同温度下测量发光效率对注入载流子密度的依赖性,并将发光效率的最大值设为内量子效率是100%,这样,其他温度点和注入载流子密度点所对应的内量子效率也就随之确定.     

基于InGaN/GaN多量子阱双波长发光二极管生长及发光性能

差分吸收激光雷达测量臭氧浓度过程中,云层信号会造成对流层臭氧浓度剧烈的抖动,带来了很大的测量误差.本文提出了一种云消除算法,该算法通过插值云层高度区域内的臭氧浓度,有效消除了对流层臭氧浓度的剧烈抖动.通过阐述其理论基础,给出了其算法关键点,即云信号的识别和云高度的精确定位.根据云层消光系数的特点,通过设定气溶胶消光系数阈值获取云层高度信息,利用累加平均有效减少噪音造成的测量误差.结果表明,在精确确定云高、云底的基础上,运用线性插值算法对臭氧测量结果进行修正,可以有效克服云层对测量结果造成的急剧起伏.     

双波长InGaN/GaN多量子阱发光二极管的光电特性

为了实现高显色指数和流明效率的白光发光二极管,在（0001）蓝宝石衬底上利用金属有机化学气相沉积系统,生长了双波长发射的InGaN/GaN多量子阱发光二极管结构.通过对不同In组分含量的双波长发射发光二极管结构的光致发光和电致发光性能进行分析,结果表明In组分含量对双波长发射发光二极管的光致发光谱的稳定性及发光效率有重要影响.此外,用双蓝光发射的芯片来激发YAG:Ce荧光粉实现了高显色指数白光发射.     

双波长InGaN/GaN多量子阱发光二极管的光电特性

为了实现高显色指数和流明效率的白光发光二极管,在(0001)蓝宝石衬底上利用金属有机化学气相沉积系统,生长了双波长发射的InGaN/GaN多量子阱发光二极管结构.通过对不同In组分含量的双波长发射发光二极管结构的光致发光和电致发光性能进行分析,结果表明In组分含量对双波长发射发光二极管的光致发光谱的稳定性及发光效率有重...     

InGaN/GaN多量子阱蓝色发光二极管的实验与模拟分析

分别采用量子阱模型和量子点模型对蓝色InGaN/GaN多量子阱发光二极管电学和光学特性进行模拟,并和实验测量结果进行了比对,结果发现,量子点模型的引入,很好地解决了I-V和电致发光二方面的实验与理论模型间符合程度不好的问题.同时,在I-V曲线特性模拟中发现,在量子点理论模型的基础上,只有考虑到载流子的非平衡量子传输效应,才能得到和实验相接近的I-V曲线,揭示着在InGaN/GaN 多量子阱发光二极管电输运特性中,载流子的非 关键词： InGaN/GaN 发光二极管 数值模拟 量子点模型     

InGaN/GaN多量子阱蓝光发光二极管老化过程中的光谱特性

系统地研究了小注入电流(＜4 mA)下InGaN/GaN多量子阱结构蓝光发光二极管的发光光谱特性在老化过程中的变化。对比老化前后的电致发光(EL)光谱,发现在注入电流1 mA下的峰值波长(peak wavelength)和半高宽(FWHM)随老化时间增加而减小,变化过程分两个阶段：前期(＜100 h)减小速度较快,而后逐渐变缓,呈现出与LEDs的发光光功率一致的变化规律,说明LEDs的等效极化电场在老化过程中减弱,这一变化和量子阱内缺陷的增加有明确的关系。通过电学特性测量发现同一结电压(V_j=1.8 V)下的结电容C_j和由交流小信号I—V方法计算得到的注入电流1 mA下的结电压V_j随老化时间增加而增大,明确了在同等小注入电流下量子阱内的载流子浓度随老化过程增加。分析表明在老化过程中InGaN/GaN 多量子阱结构蓝光发光二极管量子阱内的缺陷及其束缚的载流子数量增加,形成了增强的极化电场屏蔽效应,减弱的等效极化电场导致了量子阱的能带倾斜变小,带边辐射复合能量增大,能态密度增多,对应的发光过程的峰值波长变短(蓝移),半高宽变窄。     

图形化蓝宝石衬底上InGaN/GaN多量子阱发光二极管的光谱特性研究

运用电致发光(EL)和光致发光(PL)实验,分析了图形化蓝宝石衬底(PSSLEDs)和常规平面蓝宝石衬底(C-LEDs)InGaN/GaN多量子阱发光二极管的光谱特性。对比EL谱,发现PSSLEDs拥有更强的光功率和更窄的半峰宽(FWHM),说明PSSLEDs具有较高的晶体质量。其次,PSSLEDs的EL谱半峰宽随电流增加出现了更快的展宽,而这两种LED样品的PL谱半峰宽随激光功率增加呈现了基本相同的展宽变化,说明在相同电流下,PSSLEDs量子阱中载流子浓度更高,能带填充效应更强。另外,随着电流的增加,PSSLEDs和C-LEDs的峰值波长都发生蓝移,且前者的蓝移程度较小,结合半峰宽的对比分析,说明PSSLEDs量子阱中的极化电场较小。最后,对比了PSSLEDs和C-LEDs的外量子效率随电流的变化,发现PSSLEDs拥有更严重的efficiency droop,说明量子阱中极化电场不是导致efficiency droop的主要原因。     

InGaN/GaN多量子阱LED载流子泄漏与温度关系研究

通过测量光电流,直接观察了InGaN/GaN量子阱中载流子的泄漏程度随温度升高的变化关系。当LED温度从300K升高到360K时,在相同的光照强度下,LED的光电流增大,说明在温度上升之后,载流子从量子阱中逃逸的数目更多,即载流子泄漏比例增大。同时,光电流的增大在激发密度较低的时候更为明显,而且光电流随温度的增加幅度与激发光子的能量有关。用量子阱-量子点复合模型能很好地解释所观察到的实验现象。实验结果直接证明,随着温度的升高,InGaN/GaN量子阱中的载流子泄漏将显著增加,而且在低激发密度下这一效应更为明显。温度升高导致的载流子泄漏增多是InGaN多量子阱LED发光效率随温度升高而降低的重要原因。     

垒层厚度对InGaN/GaN多量子阱电注入发光性能的影响及机理

研究了不同垒厚对InGaN/GaN多量子阱电注入发光性能的影响及机理。实验发现,当GaN垒层的厚度从6 nm增大到24 nm时,垒厚的样品发光强度更强,而且当注入电流增加时,适当增加垒厚,可以更显著增加发光强度。进一步结合发光峰位和光谱宽度的研究表明,由于应力和极化效应的存在,当垒层厚度在6~24 nm范围内时,适当增加垒层厚度不仅会使得能带的倾斜加剧,减少电子泄露,而且也会增加InGaN阱层的局域态深度,从而改善量子阱的发光性能。     

GaN肖特基二极管的正向电流输运和低频噪声行为

首先测量了GaN肖特基二极管的正向变温电流-电压特性,研究了其电流输运机制,然后分析了在不同注入电流条件下的低频噪声行为.结果表明:1)在正向高电压区,热发射机制占主导,有效势垒高度约为1.25 eV;2)在正向低偏压区(V <0.8 V),与位错相关的缺陷辅助隧穿电流占主导,有效势垒高度约为0.92 eV (T=300 K);3)在极小电流(I <1μA)和极低频率(f <10 Hz)下,洛伦兹型噪声才会出现;电子的渡越时间取决于多个缺陷对电子的不断捕获和释放过程,典型时间常数约为30 ms (I=1μA);4)在更高频率和电流下,低频1/f噪声占主导;电流的输运主要受到势垒高度的随机波动的影响,所对应的系数约为1.1.     

Simulation study of blue InGaN multiple quantum well light-emitting diodes with different hole injection layers

InGaN-based light-emitting diodes with p-GaN and p-AlGaN hole injection layers are numerically studied using the APSYS simulation software.The simulation results indicate that light-emitting diodes with p-AlGaN hole injection layers show superior optical and electrical performance,such as an increase in light output power,a reduction in current leakage and alleviation of efficiency droop.These improvements can be attributed to the p-AlGaN serving as hole injection layers,which can alleviate the band bending induced by the polarization field,thereby improving both the hole injection efficiency and the electron blocking efficiency.     

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.     

A GaN AlGaN InGaN last quantum barrier in an InGaN/GaN multiple-quantum-well blue LED

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 recombination 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.     

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.     

The effect of junction temperature on the optoelectrical properties of InGaN/GaN multiple quantum well light-emitting diodes

Thermal effects on the optoelectrical characteristics of green InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) have been investigated in detail for a broad temperature range, from 30 °C to 100 °C. The current-dependent electroluminescence (EL) spectra, current–voltage (I–V) curves and luminescence intensity–current (L–I) characteristics of green InGaN/GaN MQW LEDs have been measured to characterize the thermal-related effects on the optoelectrical properties of the InGaN/GaN MQW LEDs. The experimental results show that both the forward voltages decreased with a slope of ?3.7 mV/K and the emission peak wavelength increased with a slope of +0.02 nm/K with increasing temperature, indicating a change in the contact resistance between the metal and GaN layers and the existence of a band gap shrinkage effect. The junction temperature estimated from the forward voltage and the emission peak shift varied from 25.6 to 14.5 °C and from 22.4 to 35.6 °C, respectively. At the same time, the carrier temperature decreased from 371.2 to 348.1 °C as estimated from the slope of high-energy side of the emission spectra. With increasing injection current, there was found to be a strong current-dependent blueshift of ?0.15 nm/mA in the emission peak wavelength of the EL spectra. This could be attributed to not only the stronger band-filling effect but also the enhanced quantum confinement effect that resulted from the piezoelectric polarization and spontaneous polarization in InGaN/GaN heterostructures. We also demonstrate a helpful and easy way to measure and calculate the junction temperature of InGaN/GaN MQW LEDs.     

Simulation of InGaN/GaN light-emitting diodes with a non-local quantum well transport model

Blue InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) are simulated by the APSYS software with a non-local quantum well transport model which is used to describe the phenomenon that carriers can fly over the quantum wells directly. The simulation results based on this model are in good agreement with the experiment and show its significant influence on the output power, carrier transport, peak wavelength and current crowding effect of the InGaN/GaN MQW LEDs, indicating that the non-local quantum well transport plays an important role in these devices.     

Simulation of InGaN/GaN multiple quantum well light-emitting diodes with quantum dot model for electrical and optical effects

We report a 2D simulation of electrical and optical characteristics of green color InGaN/GaN multiple quantum well light-emitting diodes by APSYS software with a dot-in-well model. The In-rich quantum dot-like structure in InGaN/GaN multiple quantum wells has been considered in the LED experimental data analysis. Simulation results based on the quantum dot model are in better agreement with the experimental data than those based on the purely quantum well model, indicating that the quantum dot spontaneous emission and the non-equilibrium quantum transport play important roles in the InGaN/GaN multiple quantum well light-emitting diodes.