局域表面等离激元增强型LED研究

The coupling of localized surface plasmon (LSP) and quantum wells (QWs) in the near field provides a new path for radiative recombination of the injected carriers into the LED. The enhanced the radiative recombination rate provides the probability for the development of high speed devices for visible light communication. In the coupling of LSP and semiconductor active structures, there are no clear physical pictures for the LSP evanescent wave production, feedback with the excited carriers and dissipation in the metal. In this proposal, the objective is to reveal the carrier radiative recombination mechanism in the near field of LSP. The study is based on the LEDs with the buried periodic Ag nanoparticles and micron LEDs and scanning near-field optical microscopy and time resolved photoluminescence (TRPL) measurements. The main contents include: (1) Study on the rules of radiative recombination enhancement in semiconductor QW by near field in LSP. The carrier radiative recombination and LSP feedback mechanism are studied by near field PL and TRPL measurements. (2) Study on the energy dissipation mechanism in LSP. The low dissipation and high efficiency coupling between LSP and QWs are supposed to be obtained by multiple QWs coupling and the optimization of the pitch, size and shape for nanoparticles array. (3) Study on the carrier screening on the evanescent wave field. The screening effect of excess carriers on the evanescent wave field is studied. The behaviors of the radiative, non-radiative recombination are studied in the near field under high injection level.

局域表面等离激元（LSP）与量子阱的近场耦合为LED中注入的载流子提供了新的辐射复合通道，从而增强辐射复合速率，为高速可见光通信器件提供了可能。在LSP与半导体发光结构耦合过程中，LSP倏逝波场的产生，与激发载流子的反馈作用，金属内部耗散并没有明晰的物理图像。本项目以揭示LSP近场作用下载流子辐射复合机制为目标，利用p型GaN中嵌埋的周期性纳米Ag颗粒以及微米LED等手段，开展下列研究：（1）研究半导体量子阱中辐射复合近场增强的规律，通过近场光学PL，时间分辨PL等手段对载流子辐射复合及与LSP反馈机制进行研究；（2） LSP耗散机理的研究，利用多量子阱耦合效应，及金属纳米阵列的周期、形状等的优化，实现低损耗、高效率的LSP和量子阱的耦合；（3）大注入下的倏逝波场屏蔽研究，研究过剩载流子对倏逝波场的屏蔽作用，大注入条件下的辐射复合、非辐射复合在近场中的表现。

氮化镓LED已经在照明，显示领域得到了广泛应用。但目前还存在长波长效率低和效率骤降的问题，基于LED的可见光通信（VLC）带宽很低。本项目以揭示局域表面等离激元（LSP）近场作用下载流子辐射复合机制为目标,针对LSP 倏逝波场的产生、与InGaN 量子阱中载流子辐射复合耦合机制，表面等离激元金属内部耗散机制科学问题，按计划完成了微米LED 和金属纳米结构制备，LSP 近场作用下的载流子复合机制，LSP 耗散机制，大注入下的倏逝波场屏蔽等研究。利用纳米压印和lift-off技术在p-GaN层内制备嵌入的Ag纳米颗粒阵列，通过LSP和量子阱共振，有效地增强了自发辐射速率和外量子效率的增强，Ag颗粒范围在90到200nm内都可以使发光得到增强。制备出大注入的微米LED结构，制备出了LSP增强量子阱和量子点发光的结构，进行了光致发光（PL），电致发光（EL），阴极荧光（CL）的表征，结合FDTD和微扰方法，获得了LSP与发光偶极子耦合过程，能量转移、散射、耗散的机制。发展了多偶极子与LSP作用的变量分离方法，分别用线性近似方法和微扰方法得到了电子束激发增强LSP耦合的原理，提出了相互垂直偶极子与LSP耦合增强的结构。研究了极化方向影响的局域表面等离激元与偶极子耦合机制，发现了小角度的偶极子可以同时实现较大的耦合强度（Purcell因子）及发光效率。进行了LSP与量子点、量子阱多体耦合的研究，平行的多量子点分布有利于协同发射，从而减少临近金属的量子点耗散，增强近场距离以外的量子点与LSP的耦合。本项目研究成果有效地提升大注入下LED、绿光LED的外量子效率，提高LED的调制带宽，将在半导体照明，新型显示以及可见光通信领域得到应用。