Growth and Characterization of Nitride Based Nanowire Heterostructures

半导体物理和应用的重大进展是通过降维结构取得的。直到最近，研究的大多数纳米结构都依赖于量子阱和量子点，分别具有一维和三维载流子约束的结构。最近新材料科学和应用的演示转向较少探索的纳米线，具有二维限制的结构。半导体奈米线领域似乎有很大的希望在奈米尺度上实现功能材料结构。事实上，合成高质量材料的能力和我们确定其性能的能力正在迅速提高。然而，纳米线的电学性质尚未被很好地理解，因此非常需要能够评估单个纳米线的表征方法。过去几年人们感兴趣的半导体之一是氮化镓，这是一种大带隙材料，有望将光学器件的范围扩展到可见范围。将氮化镓、氮化氮和氮化氮结合成三元和四元合金的可能性使得高性能异质结构器件的设计和实现成为可能。氮化物的晶格匹配衬底的缺失以及二元化合物之间的大晶格常数差异导致了高密度的位错，从而损害了许多器件的性能。位错的存在也使得很难确定这些材料的基本性质。制备GaN和相关异质结构的新方法显然是必要的。气-液-固生长为这些半导体及其异质结构的高度完美纳米线的形成提供了一条完全不同的途径。在本论文中，我们计划采用气-液-固相生长的方法合成基于GaN的同轴和纵向异质结构纳米线，并使用P.I.开发的先进扫描探针方法他的实验室对纳米线和单纳米线进行了电气测量。在非常基础的水平上修改和调整材料特性的可能性使得纳米技术在从物理、化学到生物学的一系列领域都具有吸引力。需要高质量的纳米结构和纳米尺度的评价方法来确定和实现这一领域的全部范围。异质结构是纳米线在任何器件应用中的关键元素，为了了解其性质和器件应用，必须以高水平的精度进行合成和表征。该方案解决了纳米结构领域的两个关键问题；先进的合成和精密的测量。本提案涉及许多学科当前感兴趣的科学和教育问题。该项目本质上是跨学科的，将基础物理和材料科学与先进工程相结合。这一组合有望为研究生和博士后提供优秀的培训。PI坚定地致力于通过研究经验加强本科教育，并鼓励本科生通过REU计划参与。他目前有两名本科生在这个领域工作，一名二年级的女研究生将参与这个项目。

Major advances in the physics and applications of semiconductors have been made through structures with reduced dimensionality. Until recently, most of the nanostructures studied relied on quantum wells and quantum dots, structures with one and three-dimensional carrier confinement, respectively. Recent demonstrations of new materials science and applications turned to the less explored nanowires, structures with two-dimensional confinement. The field of semiconductor nanowires appears to hold great promise of achieving functional material structures at the nanoscale. Indeed, the ability to synthesize high quality materials and our ability to determine their properties are improving very fast. However, the electrical properties of nanowires are not yet well understood and there is a great need for characterization methods capable of evaluating single nanowires. One of the semiconductors of interest of the last few years has been GaN, a large bandgap material that promises to extend the range of optical devices well into the visible. The possibility of combining GaN, InN, and AlN into ternary and quaternary alloys allows for the design and implementation of high performance heterostructure devices. The absence of lattice matched substrates for the nitrides and the large lattice constant differences between the binary compounds result in high density of dislocations that impair performance of many devices. The presence of dislocations also makes it difficult to determine fundamental properties of these materials. Novel methods of preparing GaN and related heterostructures are clearly needed. The vapor-liquid-solid growth offers a radically different route to the formation of highly perfect nanowires of these semiconductors and their heterostructures. In this proposal we plan to synthesize coaxial and longitudinal heterostructure nanowires based on GaN by vapor-liquid-solid growth, and to use advanced scanning probe methods developed in the P.I.'s lab to carry out electrical measurements on ensembles of nanowires and single nanowires. Intellectual Merit The possibility of modifying and adjusting properties of materials at a very fundamental level makes nanotechnology attractive across a range of fields, from physics and chemistry to biology. High quality nanostructures and nano-scale methods of evaluating them are needed to determine and realize the full scope of this field. It is also beginning to be clear that heterostructures, a key element in any device applications of nanowires, must be synthesized and characterized with high level of precision in order to understand their properties and device applications. This proposal addresses the two key problems of the field of nanostructures; advanced synthesis and sophisticated measurements.Broader Impact This proposal addresses scientific and educational issues of current interest to many disciplines. The project is interdisciplinary in nature and combines fundamental physics and materials science with advanced engineering. The combination is expected to provide excellent training for graduate students and a post-doctoral associate. The PI has a strong commitment to enhancing undergraduate education through research experiences and undergraduate students will be encouraged to participate through a REU program. He currently has 2 undergraduates working in the area and a second year female graduate student will be working on the project.