Nitride-based, nanostructured, light-emitting devices

几乎所有的项目都在很大程度上依赖于FIB的可用性，无论是直接还是间接地通过预期的实验结果。如果结构的纳米制造和样品的制备为分析研究提供了这样的可能性，那么对新的实验结果的期望将是合理的，这也影响了理论项目和建模。量子点是该研究小组的中心话题。只有在不来梅当地有FIB的情况下，才能在没有不必要的延迟和足够数量的情况下准备单个QD研究所需的结构。同样的道理也适用于透射电子显微镜样品的制备，这是成功实现预期装置的基本要求。对于直接依赖于这种设备的大量项目，FIB将得到充分利用。聚焦离子束系统不仅需要写入图案，而且还需要能够为透射电子显微镜的研究精确地指定区域。在这里考虑的先进系统中，镓离子束不仅用于图案化，而且可以在处理之前、期间和之后以几乎非破坏性的方式用相同的束以高分辨率对表面进行成像。这是很有可能的，因为氮化物是一种相当电阻的材料，这与例如II-VI半导体的情况形成了对比，在II-VI半导体中，离子损伤将不可避免地发生。详细论证1.台面刻蚀是研究单量子点的前提条件。理解能量转移到量子点的过程是对决定量子点激光的微观过程进行建模的基本要求。项目I-2中的µ-PL光谱工作直接取决于台面结构的可用性。2.为了实现光波在半导体微腔内的三维限制，必须制备具有大高径比的微柱。此任务所需的精度仅由FIB提供。这些泰勒德结构是优化器件性能和光-物质相互作用的基础研究所必需的。3.FIB技术大大加快了样品的制备速度，从而缩短了优化工艺参数的反馈时间。这将对激光项目I-1和I-2以及II-1和11-2中的结构特征大有裨益。4.透射电子显微镜研究的一个基本要求是能够从精确指定的样品位置，例如量子井或量子点的界面，制备样品的薄区域。这是传统的离子研磨难以实现的。在最先进的FIB中，二次离子可以用来对样品成像并持续监测制备过程，至少对氮基化合物不会造成额外的损害。5.通过在离子束入射点附近注入气体，可以提高刻蚀速率或在样品表面沉积层，这取决于气体、束流强度和扫描参数。6.在几个数量级上改变束流的能力是FIB装置的一个特殊特征，允许在大到20微米甚至更大的区域内最终变薄到小于100 nm。这种表面几乎平行的薄片，因此具有很大的电子透明面积，可以确定晶格缺陷的密度，比传统的离子研磨样品具有更大的统计意义。与所有设备项目的相关性是显而易见的。7.与所有其他的TEM制备方法相比，FIB工艺可以制备出已知厚度的薄膜。不同厚度的系列试件的检验对于确定应变松弛效应具有重要的价值。此外，为了进行图像模拟，必须知道试件厚度。

Nearly all of the projects depend to a significant extent on the availability of a FIB, either directly or indirectly via expected experimental results. If such a possibility for the nanofabrication of structures and the preparation of samples for analytical investigations is given, the expectation of novel experimental results will be justified, which also influence theoretical projects and modelling. Quantum dots are a central topic of the research group. The required structures for single QD studies can be prepared without undue delay and in sufficient numbers only if the FIB is available locally in Bremen. The same holds for TEM sample preparation, which is a basic requirement for a successful realization of the intended devices. The FIB will be fully exploited with regard to the large number of projects directly depending on this equipment. A focussed ion beam system is needed not only to write patterns, but also to enable the preparation of accurately specified areas for TEM investigations. In advanced systems taking into consideration here, the Ga-ion beam is not only used for patterning, but the surface can be imaged by the same beam with high resolution in a nearly non-destructive manner before, during and after processing. This is well possible for nitrides being a rather resistive material which contrasts, e.g., to the case of II-VI semiconductors where ion damage would occur unavoidably. Detailed arguments 1. Mesa etching is a precondition for the investigation of single quantum dots. The understanding of the energy transfer into the dots is a basic requirement for modelling the microscopic processes which determine quantum-dot lasing. The µ-PL spectroscopy efforts in project I-2 directly depend on the availability of mesa structures. 2. In order to achieve a three-dimensional confinement of the optical wave inside a semiconductor microcavity, micropillars with large height-to-diameter aspect ratios have to be prepared. The required precision for this task is only provided by a FIB. These taylored structures are needed for the optimization of device performance and fundamental studies of light-matter interaction. 3. The FIB technique greatly expedites the preparation of specimens for TEM, thus reducing the feed-back time for the optimization of the processing parameters. This will be of great benefit especially for the laser projects I-1 and I-2, as well as for the structural characterizations in II-1 and 11-2. 4. An essential requirement for the TEM investigations is the ability to prepare thin areas of a specimen from accurately specified sample positions, e. g. interfaces of quantum wells or quantum dots. This is difficult to achieve by conventional ion milling. In a "state of art" FIB, the secondary ions can be used to image the specimen and continuously monitor the preparation process without additional damage at least for nitridebased compounds. 5. Through injection of gases close to the point of impingement of the ion beam, it is possible either to enhance the etch rate or deposit layers onto the specimen surface, depending on the gas, the beam intensity and the scanning parameters. 6. The ability to vary the beam current over several orders of magnitude is a special feature of the FIB apparatus, allowing for a final thinning down to less than 100 nm over areas as large as 20 µm or even more. Such thin foils with nearly parallel surfaces and hence a large electron-transparent area allow for the determination of the density of lattice defects with a much greater statistical significance than is attainable with conventional ion milled specimens. The relevance for all device projects is evident. 7. In contrast to all other TEM preparation methods, FIB processing makes it possible to produce thin films with a known thickness. The examination of series of specimens with different thicknesses will be of great value for the determination of strain-relaxation effects. In addition, the specimen thickness must be known for image simulation.