AlGaN基深紫外LED光出射机制及其调控方法研究

AlGaN based deep UV LEDs are promising in wide applications such as biological detection, medical treatment, air- and water-purification and short distance communication for military uses, and are attracting much attention of researches. However，the low light extraction efficiency usually less than 8%, becomes the key issue hindering the improvement and applications of DUV LEDs. .In this project, facing the new challenges in light extracting from AlGaN-based deep UV LEDs，we plan to begin with the understanding of the mechanisms of light extraction, which evolves carrier recombination transitions, light propagation in the layers and total reflection from the surface of chip. By utilizing the theoretical and experimental researches on the band structure of quantum wells, UV light absorption and reemission from quantum wells, and special distribution of light intensity, the changes the anisotropy transition rate and light intensity distribution as well as the their relations will be revealed. Furthermore, with a newly-built method for describing the synthesized effect light emitting and propagating on the light extraction efficiency and spatial intensity distribution, we will find out the way to modulate these processes and have more amount of light extracted from front surface of DUV LEDS after optimization. Also, a study on the controlling the changes of light extraction behaviors from LED surfaces with structures of micro scale and nano scale, probably also by the aid of expectable coupling effect of SPP from the nano structure of metal and quantum wells, will performed for exploring the new physical mechanism and new method thereafter. Through the above efforts, we will not only make comprehensive understanding on the physical mechanism influencing the light extraction performance of AlGaN-based DUV LEDs, and developing the corresponding control methods, which would provide scientific basis for further improvement of device performance.

AlGaN基深紫外LED面临严重的出光效率问题，成为限制其应用的瓶颈。AlGaN量子阱结构的光出射过程受到量子阱的发光偏振特性、光传播过程和光导出过程综合作用，是LED研究面临的新课题。本项目将系统开展AlGaN量子阱能带结构、紫外光与量子阱结构相互作用、光场分布的理论计算和实验研究，明确载流子跃迁的各向异性、光强空间分布的变化规律及内在关系，建立综合发光过程和传播过程的光出射效率和光场分布的分析方法，研究量子阱能带结构调制和传播过程调制方法，设计和制备具有出光增强结构的LED外延片和芯片，通过优化结构参数，显著提高器件的正面出光；研究外延层界面微纳结构、表面等离激元耦合对光出射过程的作用，探索新型有效的提高发光效率和出射效率的方法，为实现高性能的AlGaN基深紫外LED提供基础。

AlGaN深紫外LED在生物、医疗等领域有巨大的应用前景，特别在当前新冠疫情发展的形势下，高效率的深紫外LED的制备受到了广泛的关注。但是，AlGaN基深紫外LED面临严重的出光效率限制。针对这一问题，本项目计划通过能带结构和量子态设计、光学特性分析和器件制备的紧密结合的研究，明确深紫外LED的偏振发光、传播和导出过程的关系和调控规律，建立综合的出光过程分析和结构设计方法，实现高效率的深紫外LED器件，并在AlGaN量子阱的光学偏振特性变化规律、紫外光在LED结构中的界面行为和量子阱耦合作用、AlGaN量子阱偏振发光、传播、出光过程的内在关联、调控规律和出光过程的综合分析方法等科学规律和方法方面取得进展，实现具有出光调制结构的280nm波长LED正面出光提高一倍以上等目标。. 项目研究过程中，我们首先开展了量子阱光学偏振特性、光传播过程和效率评价等分析方法的研究，建立了分析AlGaN基任意结构量子阱光学偏振特性的理论模型，形成了结合KP能带计算、FDTD及光学追迹分析、光场分布测量的系统的LED出光分析方法，初步确立了基于光提取效率分析的深紫外LED效率评价方法；取得了深紫外LED的偏振发光特性随量子阱、电子阻挡层等外延结构、载流子浓度、应力等因素的变化规律，明确了偏振发光过程、传播过程和导出过程的关联机制，得到了出射光场的分布规律；研究和制备了280nm波长的超薄量子阱结构、超薄p-GaN透射及纳米反射导电层、具有反射镜的台面、带有微纳结构的出射面等多种出光调制结构，与传统平面紫外光LED相比，正面出光效率可提高58%-525%，基于综合实施的出光研究，给出了优化的高出光效率280nm的LED结构。. 项目研究所取得深紫外LED特性分析方法、LED发光和出光调控规律、LED效率评价方法以及高光导出效率的深紫外LED结构设计思路和结果，丰富了对深紫外LED特性和变化规律的认识，对高性能AlGaN基深紫外LED研制具有重要意义。