【作者】 郑乘；

【导师】 韩民；

【作者基本信息】 南京大学 ， 材料物理与化学， 2012， 硕士

【摘要】 发光二极管(LEDs)由于其优异的光电性能,已经被广泛应用于照明、显示、光通信等领域。以GaN基发光二极管产生白光替代传统光源已被各界认可,然而目前其量子效率距离半导体照明的实际要求还有一定的距离。因此,如何提高LED的发光效率,设计制造出高亮度、高效率的LED,具有十分重要的研究与应用价值。用金属表面等离激元增强LED发光是行之有效的方法之一。本文用PECVD和ALD方法在GaN量子阱表面制备了氮化硅和氧化铝的介质层,在介质层表面通过团簇束流沉积法制备了不同覆盖率的Ag纳米粒子点阵,研究了表面等离激元耦合提高LED发光内量子效率和光取出效率的有效性,以及为实现有效耦合对介质表面金属纳米粒子点阵表面等离激元性质的调控方法。我们研究了氮化硅和氧化铝两种介质的Spacer层表面的Ag纳米粒子点阵的表面等离激元共振性质的变化规律,并通过选择氮化硅介质层并加热退火,调制Ag纳米粒子点阵的表面等离激元共振峰,实现了其与GaN量子阱的450nm发光波长的匹配。我们通过光致发光(PL)谱的测量,研究Ag纳米粒子点阵的表面等离激元对GaN量子阱量子效率的影响。设计了一种独特的综合测量配置,分析Ag纳米结构的反射、散射和消光作用对所测得量子阱PL强度的综合影响,实现了对LED发光增强系数的定量分析。我们选择5nm厚的氮化硅介质层作为LED量子阱与Ag纳米粒子点阵间的Spacer层,来研究Ag纳米粒子的表面等离激元对LED内量子效率的作用。结果表明,在适当的纳米粒子沉积量下,LED内量子效率随Ag纳米粒子覆盖率增加而提高,最高发光增强可达3倍。光致发光寿命谱的分析也表明,Ag纳米粒子覆盖率越高,辐射复合的寿命越短,速率越快,因而量子阱发光的内量子效率提高。氮化硅表面的Ag表面等离激元共振峰在450nm附近,与量子阱的发光波长匹配,会产生大量的SP-QW共振耦合模式,高的态密度及能量的耦合转移能够促进自发辐射速率提高,这是LED内量子效率提高的原因。我们以500nm厚的氮化硅介质层作为LED量子阱与Ag纳米粒子点阵间的Spacer层,来研究表面等离激元对LED光取出效率的作用。探讨了利用金属纳米结构表面等离激元对介质／空气界面上由于全内反射而产生的疏逝波的散射作用,以提高LED光取出效率的方案。并通过在三棱镜表面制备Ag纳米颗粒结构,在全内反射条件下探测其对全反射光的导出来模拟这个散射过程。结果表明,在低覆盖率时光取出效率随Ag纳米颗粒沉积量增大而提高,然而在高覆盖率情况下,光取出效率却随沉积量增加而开始降低。因此,通过设计一个合适的Ag纳米颗粒覆盖率,可使LED的量子效率达到最大提高。我们的研究表明：只要选择合适的介质Spacer层和金属纳米粒子材料,精确控制纳米粒子的尺寸、形貌及覆盖率等,就能够实现对金属表面等离激元的调制,从而提高LED内量子效率和光取出效率,使高亮度、高效率LED的实现成为可能。更多还原

【Abstract】 Light emmiting diodes (LEDs) have been widely used in lighting, display, optical communication and other fields for its excellent optical and electrical performance. It is universally believed that GaN-based LEDs for white lighting is replacing the fluorescent lamps in the near future. However, the emission efficiency of GaN-based LEDs has to be further improved for solid state lighting. Therefore, it is of great importance to improve the LEDs efficiency and thus, to realize high efficiency bright LEDs. A promising way to enhance LEDs light output is the use of surface plasmons (SPs) induced by metal/dielectric nanostructures.In this paper, a dielectric layer of silicon nitride (SixN) or alumina (Al2O3) was prepared on the surface of GaN quantum wells (QWs) by PECVD or ALD. A layer of silver nanoparticles with different coverage was then fabricated on the spacer layer by means of gas-phase cluster beam deposition. The enhancement of internal quantum efficiency (IQE) and light extraction efficiency (LEE) through effective SPs coupling, as well as the controlling of SPs properties induced by silver nanoparticle arrays on dielectric spacer layer has been investigated.We studied the surface plasmon resonance (SPR) of Ag nanoparticle arrays on SixN and Al2O3spacer layers. By selecting the silicon nitride dielectric layer and annealing process, we realized the modulation of SPs of Ag nanoparticles for the match between SPR and the luminescent wavelength of GaN-based LEDs (450nm).We also studied the influence of SPs in GaN quantum wells by the method of photo luminescence (PL) spectra measurements. A unique combinational configuration of measurements is designed to achieve quantitative analysis of LEDs emission enhancement factor, by taking into account the role of reflection, scattering and extinction of the Ag nanostructures.A5nm-thick dielectric spacer layer of silicon nitride was fabricated between the GaN quantum wells and the silver nanoparticle layer, to study the internal quantum efficiency enhancement due to the surface plasmons. The results show that, within an appropriate coverage, the IQE is increasing with the coverage of silver nanoparticles. A3-fold photoluminescence (PL) enhancement has been achieved. Time-resolved photoluminescence (TRPL) analysis provides further evidence that higher coverage of Ag nanoparticles can result in shorter lifetime and faster rate of radiative recombination, leading to the enhancement of IQE. Since SPR of silver nanoparticles on SixN layer peaks at about450nm, it results in high density of states near the QWs, which accelerates the spontaneous emission, In addition, the coupling of spontaneous emission from QWs into the SP modes can also improve the IQE of LEDs.A500nm-thick silicon nitride dielectric layer was fabricated to study the light extraction efficiency enhancement owing to surface plasmons. We proposed an approach to scatter the evanescent wave accompanying the total internal reflection (TIR) by nanoparticle arrays in order to improve LEDs light extraction efficiency. We also performed a quantitative measurement on an analogous system by fabricating silver nanoparticle arrays on a spectro-prism surface. The results show that the LEE is increasing with the coverage of silver nanoparticles at low coverage, and decreasing at high coverage as well. Therefore, the LEDs quantum efficiency can be improved by a suitable coverage tailoring of Ag nanoparticles.Our results indicate that the surface plasmons induced by metal nanoparticles can be precisely controlled, choosing a suitable dielectric spacer layer and metal material, along with tailoring the size, morphology and coverage of nanoparticles. Then high efficiency bright LEDs can be realized by improve its internal quantum efficiency and light extraction efficiency through surface plasmons.更多还原