Electronic Properties of Strained Narrow-Gap Quantum Wells

本计画主要研究以InSb/AlInSb异质结构为基础的二维电子系统之材料科学与物理。与其他III-V族材料相比，InSb的特征在于极端值，具有最小的能隙，最小的电子有效质量，最大的电子g因子，以及所有III-V族半导体中最非抛物线的导带。这些显著不同的参数使得InSb中的二维电子系统（2DES）成为GaAs基2DES的有趣替代品。虽然宿主材料可以影响嵌入式2DES的物理特性，但由于大多数材料的结晶质量相当差，因此研究替代材料中的2DES的动机很少。现在，InSb/AlxIn 1-xSb结构已经被制造成具有与GaAs/AlxGa 1-xAs结构相当的迁移率，其中首次观察到分数量子霍尔效应。这些高迁移率，加上InSb 2DES的参数空间差异很大，为这个项目提供了动力。本论文的目标是通过低温磁输运和磁光研究InSb/AlxIn 1-xSb异质外延材料的性质，并通过多种途径提高材料的质量。一个扫描探针显微镜，连接到相同的真空作为分子束外延室，将被用来评估掺杂效率和晶格失配基板上的缓冲层的有效性。原子氢源将被用来钝化生长表面和促进氧化物从InSb衬底解吸。随着材料质量的提高，电子-电子相互作用在低温2DES研究中的相对重要性将增加。磁输运实验将探索量子霍尔态到绝缘体的转变和分数量子霍尔制度中的行为。将利用磁光研究来表征InSb的能带结构，通过测量未掺杂威尔斯阱中的带间激子跃迁来确定限制势;通过分析激子跃迁、子带间共振和回旋共振来建立二维能带结构;并探测低朗道能级填充物处的电子动力学。该项目的范围广泛，需要三个共同研究者在分子束外延，磁输运实验和光学测量方面的集体专业知识之间的合作。该项目解决了材料科学领域的基础研究问题，具有很高的潜在技术相关性。该研究将为电子设备的新方面提供基础材料科学知识。在这些研究中要解决各种基本问题，拟议的实验也可能开发技术上重要的材料组合。 该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。 ***

This project addresses materials science and physics of 2DES(two dimensional electronic systems) based on InSb/AlInSb heterostructures. InSb is characterized by extreme values compared to other III-V materials, having the smallest energy gap, the smallest electron effective mass, the largest electron g-factor, and the most non-parabolic conduction band of all III-V semiconductors. These dramatically different parameters make two-dimensional electronic systems (2DESs) in InSb intriguing alternatives to GaAs-based 2DESs. Although the host material can influence the physics of the imbedded 2DES, there has been little motivation to study 2DESs in alternative materials since most are of considerably worse crystalline quality. Now that InSb/AlxIn1-xSb structures have been produced with mobilities comparable to those of GaAs/AlxGa1-xAs structures in which the fractional quantum Hall effect was first observed. These high mobilities, coupled with the vastly different parameter space of InSb 2DESs, provide the impetus for this project. The objectives are to advance the materials science of InSb/AlxIn1-xSb heteroepitaxy and to explore the properties of InSb 2DESs via low-temperature magneto-transport and magneto-optics.Several approaches will be used to improve materials quality. A scanning probe microscope, connected to the same vacuum as the MBE chamber, will be used to assess doping efficiency and buffer layer effectiveness on lattice-mismatched substrates. An atomic hydrogen source will be used to passivate the growth surface and facilitate oxide desorption from InSb substrates. Improvement of the materials quality will increase the relative importance of electron-electron interactions in 2DESs studied at low temperature. Magneto-transport experiments will explore the quantum Hall state to insulator transition and behavior in the fractional quantum Hall regime. Magneto-optical studies will be used characterize the energy band structure of InSb to determine the confinement potential through measurement of interband excitonic transitions in undoped wells; establish the two-dimensional band structure through analysis of excitonic transitions, intersubband resonance, and cyclotron resonance; and probe electron dynamics at low Landau-level fillings. The wide scope of the project requires collaboration between three co-investigators with collective expertise in molecular beam epitaxy, magneto-transport experiments, and optical measurements. %%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic devices. A variety of fundamental issues are to be addressed in these investigations, and the proposed experiments may also develop technologically important material combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***