Nanoheteroepitaxy of (In,Ga)N: Toward a Phosphor-Free White LED

0424161 SANDSGoal：拟议的研究目标是展示(In，Ga，Al)N发光二极管(LED)的亮红色(~650 nm)电致发光，该发光二极管采用由无位错应变(In，Ga)N纳米棒异质结阵列组成的有源区。意义：国家和国际固态照明计划旨在用LED替代荧光灯和白炽灯照明技术。一种发光效率为200 lm/W、色温与正午太阳相当、显色性与传统光源相当的白色LED替代技术有可能将总体电力消耗和相关发电厂排放减少10%。将离散的红色(In，Ga，Al)P LED与绿色和蓝色(In，Ga，Al)N LED相结合可能足以满足大型室外显示器的需求，但这种方法对于普通白光照明来说成本太高。今天最有希望的方法是利用蓝色或紫外光LED光与荧光粉的下转换。然而，基于荧光粉的白色LED固有的效率和寿命限制表明，将需要一种无荧光粉的替代品。方法：如果一种材料系统可以用于整个可见光光谱的发射，则可以消除荧光粉。传统的平面(In，Ga，Al)N LED异质结可以设计成从紫外光发射到黄色。然而，InN和GaN之间较大的晶格失配(10.8%)阻碍了明亮的橙色和红色LED的制造。提出的研究方案是基于这样一个概念，即纳米棒拓扑结构中的横向弹性应变消除可以扩大(In，Ga)N异质结中可以相干地容纳的晶格失配范围，从而使得能够在整个可见光谱范围内制造明亮的(In，Ga，Al)N LED。用卤化物气相外延(HVPE)和射频等离子体分子束外延生长了GaN和(In，Ga)N自组织纳米棒，而不使用异质金属催化剂，这表明用纳米棒的方法制作红色LED是可行的。这项拟议的研究将资助P.I.和他的两名研究生(一名完全致力于这一项目，另一名将与另一项需要相同技能的项目分开工作)，以确定控制HVPE、金属有机物化学气相沉积和反应脉冲激光沉积(PLD)中纳米棒生长机制的因素。我们将测试纳米异质外延的理论，并探索利用多孔阳极氧化铝模板控制纳米棒直径分布的方法。这项工作的最终目的是展示一种峰值发射波长为~650 nm(红色)的(In，Ga)N纳米棒阵列LED。P.I.和他的学生拥有从事这项研究的独特设施，包括用于合成(In，Ga)N纳米棒的定制HVPE反应堆，以及使用氨工艺气体和第三族金属靶材的负载锁定PLD系统。广泛影响跨学科研究环境：拟议的研究计划将支持研究生在跨学科环境中的研究。P.I.在普渡大学兼任欧洲教育和欧洲经济研究院，他的研究小组由欧洲教育和欧洲经委会的研究生和本科生组成，他们都积极参与了伯克纳米技术中心的工作。外展：P.I.计划对拟议的研究项目进行补充，开发一个30分钟的动手演示文稿，可以针对小学、中学和成人非专业观众进行调整。演讲的重点将是LED作为一种新兴的纳米技术成功故事，利用这些明亮的光源自然引起的感官刺激和好奇心。报告还将介绍可能受益于纳米技术的其他能源转换技术的要素，包括固态冷却，以及这些新技术对社会的潜在影响。高级设计项目：P.I.将在每年一次的MSE高级项目中引用拟议研究项目的科学和技术背景，每个学年有4-6名本科生参加。学生将利用实验室设施并与工业导师互动，设计III-V氮化物异质结构的新型生长、蚀刻和纳米制造工艺。

0424161SANDSGoal: The proposed research is directed toward the goal of demonstrating bright red (~650 nm) electroluminescence from an (In,Ga,Al)N light-emitting diode (LED) employing an active region consisting of an array of dislocation-free strained (In,Ga)N nanorod heterostructures. Significance: National and international solid-state lighting initiatives are aimed at replacing fluorescent and incandescent lighting technologies with an LED alternative. A white LED replacement technology with luminous efficiency of 200 lm/W, color temperature comparable to the midday sun, and color rendering equivalent to conventional illumination sources has the potential to reduce overall electric power consumption and the associated power-plant emissions by 10%. Combining discrete red (In,Ga,Al)P LEDs with green and blue (In,Ga,Al)N LEDs may suffice for large outdoor displays, but this approach is too costly for general white-light illumination. Today's most promising approaches utilize down-conversion of blue or UV LED light with phosphors. However, efficiency and lifetime limitations inherent to phosphor-based white LEDs suggest that a phosphor-free alternative will be required. Approach: The phosphors could be eliminated if one materials system could be utilized for emission across the entire visible spectrum. Conventional planar (In,Ga,Al)N LED heterostructures can be designed to emit from the UV into the yellow. However, the large lattice mismatch between InN and GaN (10.8%) prevents the fabrication of bright orange and red LEDs. The proposed research program is based on the concept that lateral elastic strain relief in the nanorod topology can extend the range of lattice-mismatch that can be accommodated coherently in an (In,Ga)N heterostructure, thereby enabling the fabrication of bright (In,Ga,Al)N LEDs across the entire visible spectrum. Self-organized GaN and (In,Ga)N nanorods have been grown by halide vapor phase epitaxy (HVPE) and rf-plasma molecular beam epitaxy without the use of foreign metal catalysts, suggesting that the nanorod approach to a red LED may be feasible. The proposed research will fund the P.I. and two of his graduate students (one fully dedicated to this project, and a second who will split his or her effort with another project that requires the same skill set) to identify the factors that control the nanorod growth regimes in HVPE, metalorganic chemical vapor deposition and reactive pulsed laser deposition (PLD). The theories of nanoheteroepitaxy will be tested, and methods to control the nanorod diameter distribution using porous anodic alumina templates will be explored. The work will culminate in an attempt to demonstrate an (In,Ga)N nanorod-array LED with a peak emission wavelength of ~650 nm (red). The P.I. and his students have unique facilities to pursue this research, including a custom HVPE reactor for (In,Ga)N nanorod synthesis, and a load-locked PLD system with ammonia process gas and group-III metal targets.Broader ImpactsInterdisciplinary Research Environment: The proposed research program will support graduate student research in an interdisciplinary environment. The P.I. has a joint appointment in ECE and MSE at Purdue, and his research group is evenly populated with MSE and ECE graduate and undergraduate students, all of whom are actively involved in the Birck Nanotechnology Center. Outreach: The P.I. proposes to complement the proposed research program with the development of a 30-min hands-on presentation than can be tuned for elementary, secondary and adult layperson audiences. The focus of the presentation will be on LEDs as an emerging nanotechnology success story, taking advantage of the sensory stimulation and curiosity naturally evoked by these bright light sources. The presentation will also bring in elements of other energy conversion technologies that might benefit from nanotechnology, including solid-state cooling, and the potential impacts of these new technologies on society. Senior Design Projects: The P.I. will invoke the scientific and technological contexts of the proposed research program in an annual MSE Senior Project, involving 4-6 undergraduate students each academic year. The students will utilize the laboratory facilities and interact with industrial mentors in the design of novel growth, etching and nanofabrication processes for III-V nitride heterostructures.