Nitride-based, nanostructured, light-emitting devices

几乎所有的项目都在很大程度上直接或间接地通过预期的实验结果依赖于FIB的可用性。如果结构的纳米制造和分析研究样品的制备有这种可能性，那么对新的实验结果的期望将是合理的，这也会影响理论项目和建模。量子点是研究小组的一个中心课题。只有在不来梅当地有FIB的情况下，才能毫不拖延地编制单一QD研究所需的结构和足够数量的结构。TEM样品制备也是如此，这是成功实现预期设备的基本要求。对于直接依赖这种设备的大量项目，将充分利用FIB。聚焦离子束系统不仅需要书写图案，还需要为TEM研究准备精确指定的区域。在这里考虑的先进系统中，镓离子束不仅用于图像化，而且可以在处理之前，过程中和之后以几乎无损的方式用同一束高分辨率成像表面。这是很可能的，因为氮化物是一种相当电阻的材料，这与II-VI半导体的情况形成对比，在这种情况下，离子损伤将不可避免地发生。1.详细论证台面蚀刻是研究单量子点的先决条件。理解能量转移到量子点是模拟决定量子点激光的微观过程的基本要求。项目I-2中的µpl光谱工作直接取决于台地结构的可用性。2. 为了在半导体微腔内实现光波的三维约束，必须制备具有大高径比的微柱。此任务所需的精度只能由FIB提供。这些分层结构对于器件性能的优化和光-物质相互作用的基础研究是必需的。3. FIB技术大大加快了TEM样品的制备速度，从而缩短了工艺参数优化的反馈时间。这对激光项目I-1和I-2，以及II-1和11-2中的结构表征有很大的帮助。4. TEM研究的一个基本要求是能够从精确指定的样品位置（例如量子阱或量子点的界面）制备样品的薄区域。这是传统离子铣削难以实现的。在“最先进的”FIB中，二次离子可用于对样品成像并连续监测制备过程，至少对氮基化合物没有额外的损害。5. 通过在离子束撞击点附近注入气体，可以提高蚀刻速率或在试样表面沉积层，具体取决于气体、光束强度和扫描参数。6. 在几个数量级上改变光束电流的能力是FIB设备的一个特殊功能，允许在20 μ m甚至更大的区域内最终细化到小于100 nm。这种具有几乎平行表面的薄箔，因此具有较大的电子透明面积，使得晶格缺陷密度的测定具有比传统离子研磨样品更大的统计意义。所有设备项目的相关性是显而易见的。7. 与所有其他TEM制备方法相比，FIB处理可以生产具有已知厚度的薄膜。一系列不同厚度试件的试验对确定应变松弛效应具有重要价值。此外，试样的厚度必须知道图像模拟。

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.