纳米图形化结构高效氮化镓发光器件的机理及光电特性研究

GaN and its related compounds such as AlGaN and InGaN have emerged as important semiconductor materials for high-performance light emitters in the ultraviolet (UV), blue, and green spectral regions. However, one still needs to further improve output efficiency of these GaN-based light-emitting diodes (LEDs) for applications such as solid-state lighting. Therefore, based on the fabrication methods of patterned sapphire substrate (PSS), further research of basal physical mechanism with respect to GaN epitaxial growth and light extraction efficiency shows great importance. In this project, in view of the influence of nano-pattern on the enhancement of internal quantum efficiency (IQE) and light extraction efficiency (LEE), our research is focused on the improvement of crystalline quality by nano-epitaxy. This is concerned with the nano-size nuclear layer, strain relaxation and threading dislocation bending due to PSS substrate. The droop effect of LED at high current density may be reduced due to the decrease of the stress during the nano-epitaxy. Additionally, sub-wavelength scattering effect on nano-PSS may obviously reduce the internal reflection and enhance the light extraction efficiency. Furthermore, we aim to understand the physical mechanism of light transporting, regulating and confining in the pattern epitaxial structure. Thus, the transmitting rule near the interface between the epitaxial structure and nano-PSS substrate is comprehended. With the combination of self-organized technology, the epitaxial structure with high efficiency based on the nano-PSS is designed and obtained. Finally, the LED device will be fabricated on nano-patterned substrate to realize the high light efficiency. Synchronously, some core technology of LED photoelectric device is also developed with independent intellectual property rights.

围绕图形化结构在高效功率型发光器件中的制备方法，深入研究其对材料外延生长、光提取效率相关基础物理机理，以及图形化制备技术等问题，具有重要的科学意义和应用价值。针对纳米图形化对提高LED的内量子效率和提取效率的影响，主要研究纳米外延成核、生长、应力释放机制对材料晶体质量的机理，特别是亚波长散射效应降低内全反射、图形化引起位错的弯曲、应力降低对LED器件droop效应的影响等核心问题，掌握在图形化结构中光的传播、控制和束缚的物理机制，探索出光子在图形化结构和介质界面的传播规律，并结合自组装技术，设计出基于纳米图形衬底的高效发光外延结构。最终提高发光效率，制备出纳米图形化的LED器件，开发出若干具有自主知识产权的光电器件的关键技术。

蓝宝石衬底作为发光二极管最常用的衬底，经过不断发展，重点是解决与GaN间晶格失配和热膨胀失配问题。图形化衬底技术的延展，除了能减少生长在蓝宝石衬底上GaN之间的差排缺陷,提高磊晶质量以解决失配问题,更能提高LED的出光效率。采用图形化蓝宝石衬底(PSS)技术可以降低GaN外延层材料位错密度，提高了发光二极管(LED)的内量子效率(IQE)，同时使LED光析出率(LEE)提高，基于PSS技术可以制作高效GaN基高亮度LED。本项目开展了基于纳米图形衬底上的氮化镓外延技术，研究图形衬底表面质量输运和形核机理，图形合并过程中3D应力控制以及位错的弯曲，纳米图形衬底生长工艺的优化对提高内量子效率的影响。在不影响LED电学特征的前提下，实现几种具有较高光提取效率结构的制备方法，如双面粗化、多层增透膜的等，进一步提高光提取效率80%，出光效率达到160lm/W。