【作者】 林颖；

【导师】 刘昌；

【作者基本信息】 武汉大学 ， 材料物理与化学， 2013， 博士

【摘要】 半导体照明具有高效节能,寿命长,全固态,无毒,安全性好等众多优点,已经逐渐替代了原有的照明产品并且引发了第三次照明革命。但是目前大规模产业化的白光LED由蓝光LED激发黄光荧光粉实现的,色彩还原性差,显色指数低。采用近紫外LED芯片激发红绿蓝三色荧光粉实现白光照明是一个较为理想的途径。相比蓝光LED芯片来说,近紫外芯片最关键的问题是发光效率低下的问题。利用金属表面等离子体耦合增强半导体发光是当前研究的热点问题。本文围绕制备高质量的近紫外LED量子阱和ZnO薄膜,采用金属局域表面等离子体耦合来提高其发光效率开展了如下工作：1.在理论上通过有限时域差分法(FDTD)模拟得出金属局域表面等离子体共振峰(LSPR)的位置和纳米结构的尺寸、形状和周围介质有关。在周期性的金属纳米阵列中,纳米颗粒的表面等离子体共振可以导致很强的局域电场增强。发现尺寸100nm Pt纳米颗粒的表面等离子体共振峰位于350nm左右,尺寸100nmAl纳米的表面等离子体共振峰位于380nm左右。模拟了纳米颗粒的表面电场分布,发现Al纳米颗粒的表面电场在三角形和四方形的顶点处增强达到了31倍。2.在实验上摸索掌握了金属Pt和Al微纳加工的工艺,采用热退火技术、电子束曝光和聚焦离子束技术成功地制备了一系列的Pt和Al纳米颗粒阵列。发现要想得到边缘清晰的纳米颗粒,电子束曝光机极限的加工尺寸为100nm左右,聚焦离子束极限的辅助沉积的尺寸为50nm左右。3.用原子层沉积(ALD)的方法在硅衬底上低温(200℃)生长得到了m面非极性的ZnO薄膜,其光致发光谱中和缺陷有关的可见光非常的微弱。使用电子束曝光技术在ZnO薄膜的顶端制备了三种不同形状的Al纳米颗粒阵列。发现ZnO薄膜与Al纳米颗粒耦合后带边发光都得到了很大的增强而缺陷发光变化不大。不同形状的Al纳米颗粒耦合增强的效果也不相同,四方形纳米颗粒获得了最大2.6倍的增强。4.使用射频等离子体辅助分子束外延方法,在蓝宝石衬底上外延生长了InGaN/AlGaN多量子阱。使用用透射电子显微镜(TEM)对量子阱进行了表征,得到了生长平整,界面清晰的量子阱截面图。用光致发光谱(PL)测试了量子阱的光学性能,实现了中心波长394nm的近紫外发光。在量子阱的顶端用聚焦离子束沉积了直径100nm的Pt圆柱形纳米颗粒,首次研究了近紫外波段金属LSPR与多量子阱的耦合效果。5.为了弄清发光增强与纳米颗粒形状有关的原因,进一步探讨表面等离子体耦合增强半导体发光的机理,对Al纳米颗粒耦合ZnO的样品做了时间分辨光致发光和变温光致发光的测试,并且结合FDTD模拟的表面电场分布得到如下结论：金属表面等离子体共振带来的局域电场的极大增强和由此引起的自发辐射速率的加快(内量子效率的提高)是半导体发光增强的关键因素。更多还原

【Abstract】 Solid state lighting, in which light emitting diodes (LEDs) are used, and leads to the third revolution of the human illuminative realm by means of the advantages of saving energy, environmental protection and long lifespan, etc. The combination of yellow phosphor irradiated by a blue InGaN LED is the common way to realize white light emission in industry, but with a poor color-rendering-index. In order to achieve high color-rendering-index, the near-UV LEDs have been extensively investigated. However, the synthesized white light using the near UV irradiation and RGB phosphors has a primary drawback of low efficiencies. In this study, I try to improve the efficiency of UV emissions by fabricating high quality multi-quantum wells and ZnO films and coupling with metallic surface plasmons using the following methods.1. By numerical calculation, I found investigated that the frequency and intensity of localized surface plasmon resonance (LSPR) are highly dependent on the size, shape of the nanoparticles (NPs) and the surrounding dielectric medium. In NPs arrays, the LSPR of NPs leads to very large enhancements of electromagnetic field. The finite difference time domain (FDTD) simulation shows that the LSPR peak positions of the Pt NPs and the Al NPs with a size of100nm are350and380nm, respectively, and the maximum electric field enhancement (about30times) is around the sharp tips of squares and triangles.2. The Pt and Al NPs arrays with different sizes and shapes were fabricated by thermal annealing, electron beam lithography (EBL) and focus ion beam (FIB). In order to get sharp-edged NPs, the minimum size of NPs was100nm using EBL and the minimum size of NPs was50nm using FIB.3. Nonploar m-plane ZnO films was successfully grown on Si substrates at a relative low temperature of200oC by using atomic layer deposition (ALD). Deep level emissions due to zinc interstices or oxygen vacancies were very weak. Well defined NP arrays with different shapes were fabricated on the surface of ZnO by EBL. By top excitation of the Al NP arrays coupled with ZnO, a2.6-fold enhancement of the square NPs in peak photoluminescence intensity was achieved.4. InGaN/AlGaN multi-quantum wells (MQWs) were grown on sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). The structural and optical properities of the MQWs were studied by using transmission electron microscopy (TEM) and photoluminescence (PL). The Pt NPs arrays with a diameter of 100nm were deposited on the top of the MQWs, and the coupling between the near-UV MQWs and LSPR was investigated for the first time.5. In order to understand the shape-dependent enhancements and the coupling mechanism, the time-resolved PL spectra and the temperature-dependent PL spectra were measured. Compare with the electric filed intensity of the surface, we can conclude that the local electric field enhancement and the increasing radiative decay rate made the dominant contributions to improve the band-edge luminescence.更多还原