GaN基蓝光LED外延结构的设计

发布时间：2018-04-26 08:18

本文选题：GaN + 发光二极管　；参考：《太原理工大学》2015年硕士论文

【摘要】：近年来，GaN基发光二极管(light-emitting diodes，LEDs)作为新一代固态照明光源得到了迅猛的发展。目前GaN基蓝光LED始终被热烈讨论和研究，人们所研究的热点为严重的极化效应及在大电流注入下的“效率下降”现象，它们都在很大程度上影响了发光二极管的光电性能。在三族氮化物中，有源区的极化效应会产生强大的极化电场，它会极大地改变LED的能带结构。尤其是在有源区的量子阱中，能带发生倾斜，电子和空穴分开分别局限于量子阱两侧，使得载流子参与辐射复合而发光的机会大大减小，因此降低了量子阱的发光效率。极化效应会使LED的发光波长发生红移，从而降低通过光谱所得材料组分的准确度；极化效应还会增强量子阱结构对阱宽和垒厚的依赖性。在高电流注入下，虽然可用于发光的载流子数目增加了，但LED的发光效率并没有随着注入电流的增加有所提高反而呈下降的趋势，效率下降问题已经成为限制LED发展的一个瓶颈。许多研究指出，导致效率下降的原因可能是极化效应、电子泄露、差的空穴注入、外延缺陷、俄歇复合等。因此，在高电流注入下，LED的发光效率受到了极大地限制。到目前为止，已经有很多优秀的研究团队对如何减小氮化物的极化电场及如何改善在高注入电流下的效率下降现象进行研究，期望有效改善LED的光电性能。本论文将继续寻找减小极化效应及改善效率下降的LED器件结构优化设计。本论文的研究重点在于如何有效减小InGaN LED的极化效应及有效改善效率下降现象，具体的研究内容和研究成果主要包括： 1.研究In组分梯度渐变多量子阱(MQW)结构对InGaN蓝光LED光电性能的影响。模拟结果表明，In组分梯度渐变MQW结构能够有效地减小LED有源区的极化效应，使得电子与空穴的波函数重叠率提高，提高辐射复合率，从而提高内量子效率，所以LED器件的输出功率大大地增强了。此外，效率下降现象和发光波长的稳定性也得到了显著的改善。 2.通过对LED中电子阻挡层(EBL)的能带结构进行设计，研究新设计的EBL对InGaN/GaN蓝光LED光电性能的影响，并对新设计的EBL结构进行系统地优化，找出最佳设计方案。模拟结果表明，新设计的EBL结构通过修剪极化，能够有效减小LB/EBL界面的极化效应，增强空穴注入效率和电子束缚能力，从而改善效率下降现象，提高蓝光LED的光电学性能。 3.通过对LED有源区的垒厚进行设计，研究不同垒厚设计对LED发光性能的影响。本文提出了用从n边到p边逐渐减小垒厚的结构取代相等垒厚的传统结构，，在靠近n-GaN层采用较厚的垒用于增加电子传输距离，然而在靠近p-GaN层采用较薄的垒用于减小空穴传输距离。模拟结果表明，所提出的结构能够增强空穴注入且空穴分布更均匀，从而显著增强InGaN蓝光LED的发光效率并改善高电流注入下的效率下降现象。
[Abstract]:In recent years, GaN-based light-emitting diodes (LEDs) have been developed rapidly as a new generation of solid-state lighting sources. At present, GaN based blue light LED has always been discussed and studied. The research focus is the serious polarization effect and the phenomenon of "efficiency decline" under the high current injection, which greatly affects the photovoltaic performance of GaN diodes. In three groups of nitride, the polarization effect in the active region will produce a strong polarization electric field, which will greatly change the band structure of LED. Especially in the quantum wells in the active region, the energy band is inclined and the electrons and holes are confined to the two sides of the quantum well respectively, which makes the carrier participate in the radiation recombination and the chance of luminescence is greatly reduced, thus reducing the luminescence efficiency of the quantum well. Polarization effect will make the luminescence wavelength of LED red shift, thus reducing the accuracy of the material components obtained through the spectra, and the polarization effect will also enhance the dependence of the quantum well structure on the well width and barrier thickness. Under high current injection, although the number of carriers available for luminescence increases, the luminescence efficiency of LED does not increase with the increase of injection current. The problem of efficiency decline has become a bottleneck restricting the development of LED. Many studies indicate that the reasons for the decrease in efficiency may be polarization effect, electron leakage, poor hole injection, epitaxial defects, Auger recombination and so on. Therefore, the luminescence efficiency of LED is greatly limited under high current injection. Up to now, many excellent research teams have studied how to reduce the polarized electric field of nitride and how to improve the efficiency decline at high injection current, in order to improve the photoelectric performance of LED effectively. In this thesis, we will continue to search for the optimal design of LED devices which can reduce polarization effect and improve efficiency. This thesis focuses on how to effectively reduce the polarization effect of InGaN LED and effectively improve the phenomenon of efficiency decline. The specific research content and research results mainly include: 1. The effect of in composition gradient gradient multiple quantum well (MQW) structure on the optoelectronic properties of InGaN blue light LED is studied. The simulation results show that the gradient gradient MQW structure of in component can effectively reduce the polarization effect in the active region of LED, increase the overlap rate of wave function between electron and hole, improve the radiation recombination rate and improve the internal quantum efficiency. So the output power of the LED device is greatly enhanced. In addition, the decrease of efficiency and the stability of luminous wavelength are also improved. 2. Through the design of the energy band structure of the electronic barrier layer (EBL) in LED, the influence of the newly designed EBL on the optoelectronic performance of the InGaN/GaN blue-light LED is studied, and the newly designed EBL structure is systematically optimized to find out the best design scheme. The simulation results show that the newly designed EBL structure can effectively reduce the polarization effect of the LB/EBL interface, enhance the hole injection efficiency and the electron binding ability through pruning polarization, thus improve the efficiency decline and improve the optoelectronic properties of the blue-ray LED. 3. By designing the barrier thickness of LED active region, the influence of different barrier thickness design on the luminescence performance of LED is studied. In this paper, we propose to replace the traditional structure with equal barrier thickness by decreasing the barrier thickness from the n-edge to the p-edge, and using the thicker barrier near the n-GaN layer to increase the electron transmission distance. However, a thin barrier is used near the p-GaN layer to reduce the hole propagation distance. The simulation results show that the proposed structure can enhance the hole injection and the hole distribution is more uniform, so the luminescence efficiency of InGaN blue LED can be significantly enhanced and the efficiency decline under high current injection can be improved.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN312.8

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