氮化镓基发光二极管中V坑空穴注入的研究

For GaN-based LED, Great achievements have been made in blue LED, but both green and yellow LEDs still have a lower luminous efficiency. The V-shape pits, induced from dislocations, can significantly improve the luminous efficiency of GaN-based LED. In the previous concept, the V-shaped pits can effectively screen the dislocations, and prevent carriers from non-radiative recombination. To some extent, this concept can clarify reason why the luminous efficiency of GaN-based LEDs seems to be insensitive to the dislocations. However, this concept still support the traditional view, which is that the lower the dislocation density, the higher the luminescence efficiency. Recently, we have investigated the role of V-shape pits by numerical simulation. The simulation results show V-shaped pits can not only screen dislocations, but also play an important role on promoting hole injection into the MQWs. For The V-shape pits are induced from dislocations, it can be inferred that there is an optimal value for the dislocation density. This project is focused on the hole injection relating to the V-shaped pits. Firstly, it is directly proved by experiments that the V-shaped pits can enhance the hole injection. Secondly, it is experimentally confirmed that there is an optimal value for the dislocation density. Finally, by the means of combining theory and experiment, the calculated model about V-shaped pit is established to design the structure of pits. The project will promote our understanding on GaN-based LED; also will open a new way to improve luminous efficiency of both green and yellow LED.

氮化镓（GaN）基发光二极管（LED）在蓝光波段已取得巨大成功，但其在绿、黄光等较长波段的发光效率仍然较低。由位错诱导产生的V坑可显著提高GaN基LED的发光效率。关于V坑的作用机理，前人提出了V 坑可以屏蔽位错的物理模型，在一定程度上阐明了GaN基LED发光效率对位错密度不敏感的原因；但该模型仍遵循位错密度越低，发光效率越高的传统观点。近来，本课题组通过数值计算，理论上发现：除屏蔽位错外，V坑还有增强空穴注入的作用；由于V坑是位错诱导而产生的，这使得位错密度并不是越低越好，而应存在最佳值。本项目将重点研究V坑空穴注入相关的内容。首先，实验上获得V坑增强空穴注入的直接证据；然后，实验验证位错密度存在最佳值；最后，结合实验验证，建立完善V坑空穴注入的理论计算模型，优化设计V坑结构。本项目的完成将开拓人们对GaN基LED的认识；也为绿、黄光LED的效率提升打开全新思路。

V坑是由位错诱导产生的、镶嵌于多量子阱中的一种V形缺陷。早期的研究证明V坑可阻碍载流子靠近位错,从而减少了载流子的非辐射复合，我们称此机理为“V坑屏蔽位错”物理模型。在此模型基础上，我们提出了“V坑空穴注入”模型，认为V坑除屏蔽位错以外，还可以增强空穴注入；但该模型仍停留在未完善的理论阶段，尚未有系统、严谨和直接的实验证据可供支撑，很难使人信服。本项目正是在此背景下立项的，旨在通过实验来揭示V坑空穴注入相关的物理问题，探索提高绿、黄光LED发光效率的途径。在项目执行的过程中，我们取得如下的研究成果：（1）根据实验结果，建立了双V坑模型，完善了“V坑空穴注入”物理模型。（2）通过理论和实验研究了V坑形成的三维pn结横向电场对GaN基LED性能的影响，并解释了其背后的物理机理。（3）实验研究了V坑尺寸、密度等对GaN基绿、黄光LED性能的影响，证实了位错密度存在最佳值，证明了“V坑空穴注入”模型的正确性。这些研究成果揭示了InGaN/GaN多量子阱LED中相关V坑空穴注入的重要物理机理，指出了利用位错和V坑来提升效率的发展方向。本课题的完成为GaN基长波长LED的效率提升打开了全新的思路，对LED的研究方向有重大的影响。