【作者】 赵佳；

【导师】 李康；

【作者基本信息】 山东大学 ， 光学工程， 2011， 博士

【摘要】 纳米结构是现代光电子器件的基本结构之一,半导体器件中金属-介质纳米结构在电磁场的作用下更是具有一系列与表面等离激元相关的电磁场强局域、表面拉曼增强、异常光传输、电偶极耦合等新奇的物理效应,通过计算机数值仿真技术深入研究其中的局域耦合增强效应和相关基础物理问题具有重要的科学意义和应用价值,不但为调控发光二极管的光电过程及提高电光转换效率等问题提供了新方向和新方法,同时还为我国节能减排工程提供了新思路。研究金属-介质纳米结构在电磁场中的场局域效应、能量的传输和耦合效应等基本物理问题,深刻认识和理解电磁场与金属-介质纳米结构相互作用产生的传播、局域和耦合等效应的物理规律,可以为利用金属-介质纳米结构提高发光二极管的效率提供理论指导。特别是通过对金属-介质纳米结构调控发光二极管的电光转换,近场局域,远场辐射和异常光传输的研究,掌握金属-介质纳米结构与半导体量子阱的耦合规律和调控发光二极管增强效应的机制,可以为制备高效率的大功率发光二极管提供新的思路。围绕以上科学问题,本论文紧密围绕金属-介质纳米结构和氮化镓基蓝光发光二极管,以提高发光效率为目的,以计算机模拟仿真和理论分析为手段,研究的主要内容包括：1)通过金属的色散模型结合时域有限差分方法,实现金属-介质纳米结构发光二极管的计算机数值仿真；2)通过研究发光二极管的发光原理和光电转换过程,探索提高LED发光效率的途径和相关的理论依据；3)通过麦克斯韦方程组,推导无限厚度和有限厚度金属-介质纳米结构与电磁场相互作用激发表面等离激元的基本物理性质；4)通过对金属纳米颗粒的电磁场数值仿真,研究金属-介质纳米结构表面等离激元局域耦合效应增强电偶极的发光效率,并验证数值仿真方法的正确性；5)通过对金属薄膜在发光二极管中的理论分析和电磁场数值仿真,研究金属-介质纳米结构表面等离激元局域耦合效应增强发光二极管发光的物理过程及增强因子对金属薄膜发光二极管结构参数和材料参数的依赖；6)根据金属薄膜发光二极管结构参数和材料参数对发光强度影响的规律,并结合理论分析和数值仿真结果,对银膜氮化镓基蓝光发光二极管的结构进行参数优化。本论文主要通过计算机数值仿真,研究金属-介质纳米异质结构中的局域耦合效应及其在提高光电转换器件效率中的作用。并紧密结合国民经济和社会发展过程中与节能减排、环境保护相关的关键技术,通过在发光二极管中构筑具有特殊场耦合效应的金属-介质纳米结构,在深入研究电偶极发光和表面等离激元之间相互作用物理机理及控制规律的基础上,探索提高蓝光二极管内量子效率的新方法,为实验和生产提供思路和方向。根据上述研究内容和目标,本论文的创新工作共分为以下几个部分：Ⅰ.通过金属色散模型实现了金属-介质纳米结构在发光二极管中的三维时域有限差分方法的数值仿真。针对倒装氮化镓基蓝光发光二极管的发光和材料特性,引入纳米金属薄膜建立了数值仿真模型,并验证了方法的正确性。Ⅱ.根据发光二极管的发光原理和特性分析了各种提高发光效率的途径,针对提高内量子效率,通过对Purcell效应和金属表面等离激元电磁场特性的分析,为金属表面等离激元增强电偶极发光提高发光二极管内量子效率建立了理论依据。Ⅲ.利用金属纳米颗粒使电偶极辐射得到了近千倍的增强,根据仿真结果获得了电偶极辐射增强与金属纳米颗粒的材料和结构参数的关系,获得了金属纳米颗粒的半径、长度、环境等因素影响辐射增强的规律,并通过填充电介质的方法获得了更有效控制金属纳米颗粒共振波长的手段,充分证实了金属纳米颗粒的表面等离激元不仅可以通过域场应用Purcell效应引起电偶极辐射增强,而且具有异常光传输特性,为金属-介质纳米颗粒增强LED发光奠定了理论基础。Ⅳ.在无限厚度金属表面等离激元色散特性的基础上,对有限厚度金属薄膜两侧为同种介质和异种介质的情况下表面等离激元色散特性进行了分析和修正。并在氮化镓基蓝光发光二极管中引入金属薄膜,通过仿真结果验证了对无限厚度金属和有限厚度金属薄膜的表面等离激元电磁特性的理论分析和研究,获得了金属薄膜和发光二极管材料参数及结构参数对发光增强影响的规律,并通过优化参数在蓝光波段内得到了很高的自发辐射增强及17倍的发光增强。本论文选题来源于国家重点基础研究发展计划项目：金属/介质纳米异质结构中的局域耦合效应及其在光电转换器件中的应用。通过对金属-介质纳米结构在发光二极管中局域耦合效应的数值仿真研究,加深了可见光与金属相互作用的认识和理解,为研发具有新技术、新工艺、新流程的高亮度蓝光/白光发光二极管提供了思路和方向,为利用金属-介质纳米结构增强发光二极管发光提供了理论依据和创新的可能。更多还原

【Abstract】 Nano structures have been serving as fundamental components in contemporary optoelectronic devices. Upon interactions with electromagnetic field, nano structures on metal-dielectric interface in semiconductor devices particularly demonstrate new physical properties, in aspects like localized electromagnetic field, surface Raman enhancement, extraordinary optical transmission and coupling process related to surface plasmon. Thus intensive studies on the local coupling effect and corresponding fundamental physical problems, by means of computer numerical simulations, have great values in science and for potential applications. This not only provides new approaches to modulate the optoelectronic process and increase the electro-optical conversion efficiency in LEDs, but also enlightens a new way of energy saving and emission reduction.Focusing on metal-dielectric nano structures and electro-optical device GaN based LED, this dissertation investigates the fundamental physical problems such as local coupling, energy transmission and conversion within metal-dielectric nano structures by computer simulation and theoretical analysis, to get a profound understanding concerning the physical mechanisms responsible for electromagnetic wave propagation, localization and coupling on metal-dielectric nano structures. It contributes in providing theoretical guidance to increase the efficiency of LEDs through local coupling effect.Especially, this dissertation opens new paths to fabricate high efficiency LEDs. For this purpose, it studies how to increase the light emission of LED with adjusting and controlling the electic-optic conversion, near field localization, far field emission, extraordinary optical transmission by metal-dielectric nano structures. Then the adjusted mechanism, the coupling law between SPPs and semiconductor QWs are obtained.Around the above scientific topics, for the purpose to improve light emission efficiency, by using computer simulation and theoretical analysis, this dissertation studies on the related characteristics on metal-dielectric nano structures and GaN blue LED, and covers the following aspects:1) Computer simulation of LED containing metal-dielectric nano structures by using FDTD method and metal dispersion model;2) Exploration of approaches to increase the efficiency of LEDs by investigating the light emitting mechanism and electro-optical conversion processes in LEDs;3) Deriving from Maxwell’s equations the physical characteristics of surface plasmon on infinitely and finitely thick metal-dielectric nano structures inside a electromagnetic field;4) Verification of the enhancement of electric dipole light emission through metal-dielectric nano structures by the surface plasmon local coupling effects on metal nano particles, and the validity of the numerical methods in the study of electric dipole emission enhancement;5) Introduction of easy-to-make silver film in GaN based LED to enhance light emission after investigation of the physical process of electric dipole emission enhancement by surface plasmon local coupling effect on metallic thin film surface and the dependence of enhancement factor on material and structural parameters.6) Optimization of structural parameters after combination of obtained simulation results with theory as well as based on the fact of better enhancement effect with silver thin film in GaN LEDs than with metallic reflectors.The main purpose of this dissertation is to numerically investigate the local coupling effect in metal-dielectric nano structures and its applications to the enhancement of electro-optical conversion efficiency. In close combination with key technologies in energy saving and emission reduction, environment protection in national economy and social developments, by introducing metal-dielectric nano structures and field coupling effect in LEDs and investigating the mechanism and controlling law of electric dipole light emission interacting with surface plasmon, this dissertation explores new approaches to increase the internal quantum efficiency of blue LEDs, and serves as the guidelines for experiments and manufacture. According to the above research objects and purposes, this dissertation is organized into the following innovation parts:Ⅰ. The 3D FDTD simulation of metal-dielectric nano structures in LED is realized with modified Drude model. A numerical simulation model is established to study the light emission and the characteristics of flip-chip GaN based LEDs containing metal nano thin film, and the validity of the method is verified.Ⅱ. According to the working principles and characteristics of LEDs, the approaches to increase lighting efficiency are analyzed. In order to increase internal quantum efficiency, based on the theoretical derivation of Purcell’s effect and the characteristics of the electromagnetic field of metal surface plasmon, the theoretical foundation is established to increase the internal quantum efficiency of LEDs by metal surface plasmon enhanced electric dipole light emission.Ⅲ. With metal nano particles, the emission of electric dipole is enhanced by nearly a thousand times. According to the simulation results, the relation between the enhancement factor and the material and structural parameters of metal nano particles is concluded. It is well established that the localized field of surface plasmon on metal nano particles can enhance the emission of electric dipole by Purcell’s effect.Ⅳ. Based on the analysis of dispersion relation of surface plasmon from a infinitely thick metal, the dispersion characteristics of finitely thick metal films sandwiched between dielectrics of the same type and/or different types are analyzed and modified. Metallic film is introduced into GaN based LEDs, and the theoretical derivation of the electromagnetic characteristics of the infinitely thick metal and finitely thick metal film is verified according to the simulation results. The dependence of light emission enhancement on the material and structural parameters of metallic film and LED is concluded. After optimization,17 fold enhancement of light emission is obtained in blue light region.The work in this dissertation is supported by National Fundamental Program of China. Through numerical simulation research on local coupling effect in LEDs based on metal-dielectric nanostructures, this work has deepened the knowledge and understanding on the interactions between visible light and metals. It also sheds light on development of high brightness blue/white LEDs with new technology, new engineering, and new process, and provides theoretical background to enhance light emission of LEDs with metal-dielectric nano structures.更多还原