Nanostructure Technology for Making Photonic Crystals

电磁波在多维周期结构中的传播与电子波在真实晶体中的传播之间的类比，已被证明是非常富有成果的。最初的努力是受到“光子带隙”前景的激励；三维介质结构中的一个频带，在这个频带中电磁波被禁止，与空间中的传播方向无关。这些三维周期性介电结构通常被称为“光子晶体”。这些材料在光电子领域很有用，比如所谓的“零阈值激光器”和单模发光二极管的电磁微腔。这种结构将表现出抑制自发发射，这可以降低功率要求并提高可靠性，特别是光学阵列。另外，这种结构可以显示增强的自发发射，这将允许光互连的更快调制速度。制造业越来越多地由制造小物件组成。今天的许多技术都是在微观尺度上进行二维图形化的结果。在这个提议中，重点是制造有价值的三维纳米结构，即光子晶体的技术。三维纳米制造是一项极具挑战性的工作。这个项目开始于1993年9月。经过最初紧张的设备购置、安装和测试阶段，电子束写入器、光学诊断探针、化学辅助离子束蚀刻器和其他薄膜加工设备，第一批光子晶体于1995年初制成。在这个项目的这一点上，在光学波长的三维光子带隙的初始光学证据已经被检测到。合适的优值是三维禁隙内的反射率。观察到的光子晶体的透射光谱形状与预期接近，但到目前为止，最佳中隙实验反射率仅为~80%。虽然这已经足以开始监测光子带隙对自发光发射装置的影响，但肯定需要进一步的改进。提高光子带隙内的反射率将要求纳米结构具有更高的结构精度。如果获得资助，工作计划将包括以下内容：(a)多离子束蚀刻，其中3个离子束方向同时发射，而不是目前的顺序蚀刻步骤系统，从单个离子束开始，被多个样品旋转打断。(b)化学辅助离子束蚀刻过程中孔直径的光反馈控制。(c)建造并使用三维离子束掩膜结构。(d)如果需要，光子晶体的三维厚度将通过堆叠纳米结构层来建立，这些纳米结构层通过外延提升分离，通过表面张力技术排列，然后通过晶圆融合程序重新粘合。(e)三维纳米加工技术将扩展到InP，其电子/空穴表面复合特性足够有利，可以创造微小的，电泵浦的发光设备。与此同时，我们的合作者、加州理工学院的Axel Scherer教授也提交了一份内容大致相同的更新提案。这笔资金将允许加州大学洛杉矶分校和加州理工学院的联合努力继续发展制造光学波长尺度的三维光子晶体结构的技术，并提高这些结构的结构精度和中缝反射率。这种精细的光子晶体结构应该可以应用于光电子技术，而且它们可能在光学科学中具有普遍的用途。该NSF提案的总体范围不会改变，但要求的金额将分别减少到6万美元/年（从最初的11万美元/年），以允许这些功能将由陆军研究办公室通过预期的MURI合同提供支持。ARO和NSF的工作将沿着以下路线划分：我们雄心勃勃的计划所需的大量设备开发和建设将通过陆军MURI提供支持，而研究生和本科生的大部分培训将主要通过加州大学洛杉矶分校的NSF资助来建造、使用和维护这些设备。定义和评估三维光子晶体所必需的复杂过程将为我们的学生在这个项目中工作提供一个很好的机会，使他们熟悉使用和维护各种先进的制造设备。我们建议大部分的工艺开发和优化以及学生培训将导致先进的三维光子晶体的定义将在NSF的提议下完成。另一方面，这项工作所需的设备制造和设备建设将由陆军MURI提供支持。被排除在NSF项目之外的将是更近期的任务导向项目，如微波光子晶体、将二维光子晶体作为边缘发射激光二极管的端镜、用于形成双折射计算机生成全息图的深光栅的定义，以及高对比度偏振分束器的开发（测量的TE/TM对比度超过300:1）。因此，NSF支持项目的具体任务是：1。三种离子源多离子束蚀刻系统的设计。开发新的三维掩蔽方法以制造更厚的光子晶体。3. 利用外延发射技术制造厚光子晶体的机械堆叠方法的发展。4. 基于光子晶体的新型光电器件的设计与建模。5. 大面积替代光刻技术的发展，如通过电化学自组装。所有这些任务都将在研究生和本科生的帮助下完成，他们将接受微加工惯例、光学测量技术和光子晶体光学现象的数值模拟方面的培训。研究生将直接获得资助，而本科生将通过暑期项目、毕业论文和在实验室的工作学习经验来接触这种最先进的设备。* * *

9632651 Yablonovitch The analogy between electromagnetic wave propagation in multi-dimensional periodic structures, and electron wave propagation in real crystals, has proven to be a very fruitful one. Initial efforts were motivated by the prospect, of a "photonic bandgap"; a frequency band in 3-dimensional dielectric structures, in which electromagnetic waves are forbidden, irrespective of propagation direction in space. These 3-dimensionally periodic dielectric structures are frequently called "photonic crystals". These can be useful in opto-electronics as electromagnetic micro-cavities for so-called "zero-threshold lasers" and single-mode light emitting diodes. Such structures would exhibit inhibited spontaneous emission, which could lower the power requirements and increase reliability, particularly of optical arrays. Alternately, such structures can show enhanced spontaneous emission which would allow faster modulation speeds for optical interconnects. More and more often, manufacturing consists of making small things. Much of today's technology is the consequence of 2-dimensional patterning on a microscopic scale. In this proposal, the emphasis is on the technology for making valuable 3 dimensional nanostructures, namely photonic crystals. Three dimensional nano-fabrication is an extraordinarily challenging undertaking. This project began in September of 1993. After an intense initial period of equipment acquisition, installation, and testing, of; electron beam writers, optical diagnostic probes, chemically assisted ion beam etchers, and other thin film processing apparatus, the first photonic crystals were made in early 1995. At this point in the project, the initial optical evidence for a 3-dimensional photonic bandgap at optical wavelengths has been detected. The appropriate Figure-of-Merit is the reflectivity within the 3-d forbidden gap. The observed shape of the optical transmission spectrum of the photonic crystal is close to expectations, but thus far the best midgap experimental reflectivity is only ~80%. While this is already sufficient to begin monitoring the effect of the photonic bandgap on spontaneous light emission devices, further improvements will definitely be needed. Improved reflectivity within the photonic bandgap will demand a higher degree of structural precision in the nanostructure. If funded, the work program would include the following: (a) Multiple ion beam etching, in which 3 ion beam directions fire simultaneously, as opposed to the current system of sequential etching steps, from a single ion beam, interrupted by multiple sample rotations. (b) Optical feedback control of the hole diameters during the chemically assisted ion beam etching. (c) 3-d ion beam mask structures will be built and used. (d) If needed, the 3-d thickness of the photon crystal will be built up by stacking nano-structure layers which are separated by epitaxial liftoff, aligned by surface tension techniques, and then rebonded by wafer fusion procedures. (e) 3-d nano-machining technology will be extended to InP, whose electron/hole surface recombination properties are favorable enough to allow the creation of tiny, electrically pumped, light emitting devices. This renewal proposal is being submitted in parallel with a substantially identical one by our collaborator Prof. Axel Scherer of Caltech. Funding would allow continuation of the joint UCLA/Caltech effort to develop the technology for making 3-dimensional photonic crystal structures at the scale of optical wavelengths, and to improve the structural precision and midgap reflectivity of these structures. Such refined photonic crystal structures should lend themselves to opto-electronic technology, and they might be generically useful in optical science. REVISED WORK STATEMENT The overall scope of this NSF proposal will not change, but the amount requested will be diminished to $60K/year respectively (from an original request for $110K/yr.), to allow for th ose functions which will be supported by the Army Research Office through an anticipated MURI contract. The ARO and NSF efforts will divide along the following lines: Extensive equipment development and construction necessary for our ambitious program will be supported through the Army MURI, whereas most of the training of both graduate and undergraduate students to build, use and maintain this equipment will be primarily funded through this NSF grant at UCLA. The complex process which is necessary for defining and evaluating 3-d photonic crystals will provide our students working on this project with an excellent opportunity to become well acquainted with using and maintaining a wide repertoire of advanced fabrication equipment. We propose that much of the process development and optimization as well as student training which will lead to the definition of advanced 3-d photonic crystals will be done under the NSF proposal. On the other hand, the device fabrication and construction of the equipment necessary for this effort will be supported by the Army MURI. Excluded from the NSF project will be more near term mission oriented projects, such as microwave photonic crystals, the inclusion of 2-dimensional photonic crystals as end-mirrors on edge-emitting laser diodes, the definition of deep gratings used to form birefringent computer generated holograms, and the development of high-contrast polarizing beam-splitters (with measured TE/TM contrast ratios in excess of 300:1). Thus, the specific tasks performed for the NSF supported program will be: 1. The design of a multiple ion beam etching system with three ion sources, 2. The development of new three-dimensional masking procedures to make thicker photonic crystals. 3. The development of mechanical stacking procedures using epitaxial liftoff for thick photonic crystal fabrication. 4. The design and modeling of new optoelectronic devices based on photonic crystals. 5. The development of altern ative lithography techniques over large areas, such as through electrochemical self-assembly. All of these tasks will be performed with the help of graduate and undergraduate students, who will be trained in microfabrication conventions, optical measurement techniques, and numerical modeling of optical phenomena in photonic crystals. Graduate students will be directly supported by the grant, whereas undergraduates will be exposed to this state of the art equipment through summer programs and senior thesis and workstudy experience in the laboratory. ***