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

[0424161sands]目标：提出的研究目标是通过采用由一系列无位错应变（In,Ga）N纳米棒异质结构组成的有源区域，展示（In,Ga,Al）N发光二极管（LED）的亮红色（~650 nm）电致发光。意义：国家和国际固态照明倡议旨在用LED替代荧光灯和白炽灯照明技术。白光LED替代技术的发光效率为200lm /W，色温与正午太阳相当，显色性与传统照明光源相当，有可能减少总电力消耗和相关发电厂排放10%。将分立的红色（In,Ga,Al）P led与绿色和蓝色（In,Ga,Al）N led相结合，可能足以满足大型户外显示器的需求，但这种方法对于一般的白光照明来说过于昂贵。目前最有前途的方法是利用荧光粉对蓝色或UV LED光进行下转换。然而，基于磷的白光led固有的效率和寿命限制表明，将需要一种无磷的替代品。方法：如果可以利用一种材料系统在整个可见光谱上发射，则可以消除荧光粉。传统的平面（In,Ga,Al）N LED异质结构可以设计成从紫外光发射到黄光。然而，InN和GaN之间的大晶格不匹配（10.8%）阻碍了明亮橙色和红色led的制造。提出的研究计划是基于这样的概念：纳米棒拓扑结构中的横向弹性应变可以扩展（in,Ga）N异质结构中可容纳的晶格不匹配范围，从而能够在整个可见光谱中制造明亮的（in,Ga,Al）N led。通过卤化物气相外延（HVPE）和射频等离子体分子束外延（rf-plasma molecular beam外延）制备出了自组织GaN和（In,Ga）N纳米棒，而无需使用外来金属催化剂，这表明纳米棒方法制备红色LED是可行的。拟议的研究将资助P.I.和他的两个研究生（一个完全致力于这个项目，另一个将把他或她的努力与另一个需要相同技能的项目分开）来确定控制HVPE纳米棒生长机制的因素，金属有机化学气相沉积和反应性脉冲激光沉积（PLD）。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。这项工作将在尝试展示一个峰值发射波长为~650 nm（红色）的（in,Ga）N纳米棒阵列LED时达到高潮。P.I.和他的学生拥有独特的设施来进行这项研究，包括用于（In,Ga）N纳米棒合成的定制HVPE反应器，以及带有氨过程气体和iii族金属靶的负载锁定PLD系统。更广泛的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.在普渡大学的欧洲经委会和MSE有一个联合任命，他的研究小组由MSE和欧洲经委会的研究生和本科生组成，他们都积极参与伯克纳米技术中心。外联：私家侦探建议通过开发一个30分钟的实践演示来补充拟议的研究计划，该演示可以针对小学，中学和成人外行观众进行调整。演讲的重点将是led作为新兴纳米技术的成功案例，利用这些明亮的光源自然唤起的感官刺激和好奇心。该演示还将介绍可能受益于纳米技术的其他能量转换技术的元素，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.将在年度MSE高级项目中引用拟议研究项目的科学和技术背景，每学年涉及4-6名本科生。学生将利用实验室设施，并与工业导师互动，设计III-V型氮化物异质结构的新型生长，蚀刻和纳米加工工艺。

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.