GaN基纳米柱LED选区外延及相关光电基础科学问题研究

In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nanoelectronics and nano-photonics. Compared to conventional 2 D thin film LEDs, Nanorod LED has many merits, such as low dislocation density, weak polarization effect, large emission area and high saturation current, which has been thought to be a breakthrough development in solid state lighting. However, the external quantum efficiency (EQE) of nanorod LED is still far lower than that of conventional LED due to the great difficulty of 3 D InGaN/GaN growth. In the project, we plan to grow high quality of GaN nanorods on the nano-pattern template fabricated by nanospherical-lens photolithography (NLP) technology, followed by the growth kinetics of metal organic chemical vapor deposition (MOCVD). The annihilation mechanism of the threading dislocation (TDs), distribution of stress and energy band of InGaN/GaN nanorod structures are investigated. With the combination of theory simulation and experiment results, the carrier transport and recombination physical course in many quantum wells (MQWs) are understood in nanorod LED. Additionally, the critical reasons with respect to the efficiency droop of nanorod LED at high current are also comprehended. Furthermore, we also investigate the transport behavior of photons in nanorod and present the model of photon-phonon coupling by using the finite-difference time-domain simulation (FDTD). To resolve the problem of current spreading, we also use the graphene as the transparent electrode to replace the polymer medium and the ohmic contact between graphene and p-GaN of nanorod LED is detailedly analyzed to understand the physical mechanism. Finally, we wish the our results may provide the theoretical and experimental supports for the research of nanorod LED, to push the nanorod LED into the market of solid state lighting.

相比于传统平面结构LED，纳米柱LED具有低位错、弱极化、大的发光面积和高饱和电流等诸多优势，是未来半导体照明效率进一步提高的重要技术路线，具有重要的研究价值。然而，受困于3D纳米结构生长的困难，纳米柱LED效率与传统LED仍存在很大差距。本项目拟在纳米球镜光刻制备的模板上选区外延纳米柱LED，研究3D纳米柱结构动力学生长规律，揭示低维InGaN/GaN材料的位错增殖、应力分布和能带结构，构建3D纳米结构载流子输运复合模型，掌握纳米柱LED高注入下Droop物理机制。本项目将探索纳米柱结构中光子传输行为研究，建立光子耦合发射理论模型，阐述3D纳米结构独特的发光特性。此外，也将采用新型石墨烯透明电极来解决纳米柱LED电流扩展的问题，研究其欧姆接触机理，进一步提高纳米柱器件量子效率。本项目的预期成果是为纳米柱LED研究提供理论基础和实验储备，从而推动纳米柱LED尽快进入半导体照明市场。

相比于传统平面结构LED，纳米柱LED具有低位错、弱极化、大的发光面积和高饱和电流等诸多优势，是未来半导体照明效率进一步提高的重要技术路线，具有重要的研究价值。然而，受困于3D纳米结构生长的困难，纳米柱LED效率与传统LED仍存在很大差距。本课题围绕选区外延生长GaN纳米柱LED材料和器件中的基础科学问题，特别是针对纳米柱中3D应力驰豫机制和位错演变规律，系统研究了3D纳米柱结构GaN的可控生长，结合能带模拟，探索了纳米柱InGaN/GaN多量子阱立体分布特性和载流子复合机制。客服了3D结构生长均匀性差和器件易漏电的难题，采用Wolf模型解释了纳米柱LED生长机理，通过控制生长条件获得In组分在纳米柱侧壁的变化，获得无荧光粉白光LED。进一步结合量子点，实现显色指数达到87的无荧光粉白光金字塔LED。同时借助APSYS和FDTD，对3D结构的载流子输运和光子耦合机制进行了深入研究，实现了提高纳米柱LED外量子效率的有效方法，获得内量子效率达到81%的280nm深紫外纳米柱LED，消除了TM光学偏振的影响，光提取效率较平面结构提高2.5倍，获得深紫外器件的电致发光。课题研究为纳米柱LED研究提供理论基础和实验储备，推动新型照明的发展。