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.     

Simulation of InGaN/GaN light-emitting diodes with patterned sapphire substrate

Blue InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with patterned sapphire substrate (PSS) are simulated by the APSYS software. Approach of combining finite-difference time-domain (FDTD) method and raytracing technique is applied to perform light extraction. The simulation results show that PSS dramatically increases extraction efficiency of light power, in agreement with experiment. It is found that extraction efficiency can be maximized by changing the shape of PSS. This work presents a new approach to combine electrical simulation with FDTD and raytracing in 3D TCAD simulation of GaN-LED.     

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     

Investigation of blue InGaN light-emitting diodes with step-like quantum well

The concept of a step-like quantum well is proposed with the purpose to reduce the influence of electrostatic field resulting from the piezoelectric effect on the optical performance of blue InGaN light-emitting diodes. Particularly, the optical properties of the LED structures with the In_0.23Ga_0.77N single quantum well, In_0.20Ga_0.80N/In_0.26Ga_0.74N step-like quantum well, and In_0.26Ga_0.74N/In_0.20Ga_0.80N step-like quantum well are numerically investigated in detail. Simulation results show that the In_0.20Ga_0.80N/In_0.26Ga_0.74N step-like-quantum-well LED structure has the best optical performance in virtue of the improvement in spatial overlap of electrons and holes in the quantum well.     

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.     

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.     

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.     

InGaN/GaN多量子阱结构发光二极管发光机理转变的低频电流噪声表征

本文对InGaN/GaN多量子阱结构发光二极管开启后的电流噪声进行了测试, 结合低频电流噪声的特点和载流子之间的复合机理, 研究了低频电流噪声功率谱密度与发光二极管发光转变机理之间的关系. 结论表明, 当电流从0.1 mA到10 mA逐渐增大的过程中, InGaN/GaN发光二极管的电流噪声行为从产生-复合噪声逐渐接近于低频1/f噪声, 载流子的复合机理从非辐射复合过渡为电子与空穴之间载流子数的辐射复合, 并具有标准1/f噪声的趋势, 此时多量子阱中的电子和空穴之间的复合趋向于稳定. 本文的结论提供了一种表征InGaN/GaN多量子阱发光二极管发光机理转变的有效方法, 为进一步研究发光二极管中载流子的复合机理、优化和设计发光二极管、提高其发光量子效率提供理论依据.     

Droop improvement in blue InGaN light-emitting diodes with GaN/InGaN superlattice barriers

GaN/InGaN superlattice barriers are used in InGaN-based light-emitting diodes （LEDs）. The electrostatic field in the quantum wells, electron hole wavefunction overlap, carrier concentration, spontaneous emission spectrum, light-current performance curve, and internal quantum efficiency are numerically investigated using the APSYS simulation software. It is found that the structure with GaN/InGaN superlattice barriers shows improved light output power, and lower current leakage and efficiency droop. According to our numerical simulation and analysis, these improvements in the electrical and optical characteristics are mainly attributed to the alleviation of the electrostatic field in the active region.     

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.     

3D simulation of InGaN/GaN micro-ring light-emitting diodes

We employed the APSYS software to perform 3D electrical and ray-tracing simulations on micro-ring light-emitting diodes (LEDs) to verify previous experimental findings that they have higher extraction efficiency than micro-disk and broad area LEDs. 3D ray-tracing indicates the importance of inter-ring optical interactions. Furthermore we found that the higher light extraction efficiency is at the expense of reduced internal quantum efficiency (IQE) as injection current is increased.     

Blue InGaN light-emitting diodes with dip-shaped quantum wells

InGaN based light-emitting diodes (LEDs) with dip-shaped quantum wells and conventional rectangular quantum wells are numerically investigated by using the APSYS simulation software. It is found that the structure with dip-shaped quantum wells shows improved light output power, lower current leakage and less efficiency droop. Based on numerical simulation and analysis, these improvements on the electrical and the optical characteristics are attributed mainly to the alleviation of the electrostatic field in dip-shaped InGaN/GaN multiple quantum wells (MQWs).     

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.     

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     

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.     

Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes

In this study, the influence of multiple interruptions with trimethylindium(TMIn)-treatment in InGaN/GaN multiple quantum wells(MQWs) on green light-emitting diode(LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence(PL) full-width at half maximum(FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence(EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment.     

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.