Quantum Confined Electron Systems in Coherently Strained Si-Ge Nanowire Heterostructures

非技术描述：半导体异质结构在许多科学发现和技术进步中发挥着重要作用。虽然大多数研究都集中在平面异质结构上，但非平面异质结构，特别是纳米线，最近引起了人们的极大兴趣。这项研究项目解决了非平面半导体异质结构，特别是硅-锗核-壳纳米线的加工和表征的基本问题。这些研究活动旨在增进材料合成和表征方面的知识，从而有助于未来高速、低功耗电子器件的设计。研究活动与学生的前沿研究教育和培训很好地结合在一起。更具体地说，这项工作为研究生和本科生提供半导体生长、制造和表征技术方面的教育，研究成果被整合到课程材料和面向高中生的外展讲座中，以鼓励在科学、技术和工程领域的职业生涯。技术描述：半导体纳米线提供了一个实现外延、非平面异质结构的通用平台，与基础科学和技术应用相关。本研究项目的主要目标是(1)通过结合能带工程和调制掺杂来促进IV族纳米线的生长，(2)表征其结构和电子性质，(3)实现和探索相干应变Si-SiGe核壳纳米线中的量子受限电子系统。更具体地说，这些纳米线异质结构是采用气-液-固三相法生长的硅纳米线核心和超高真空化学气相沉积外延的SiGe外壳相结合的方法生长的。利用微拉曼光谱与晶格动力学理论相结合的方法，对Si-Ge核壳纳米线的应变分布进行了实验研究，并与理论计算结果进行了比较。制备了基于纳米线异质结的低阻接触场效应管，并在低温下对其进行了表征，以确定其电子迁移率，并将其与纳米线异质结设计相关联。将能带工程和径向调制掺杂相结合，提高了Si-SiGe核壳纳米线中一维电子的迁移率。利用自洽密度模拟和实验纳米线电导对密度的依赖关系，提取了Si-SiGe核壳纳米线中核壳之间的能带偏移量。实验研究了Ge-SiGe核壳纳米线中高迁移率一维空穴系统的磁输运特性，重点研究了自旋分裂和自旋-轨道相互作用，以评估是否可以在实验上观察到具有排列的自旋和动量的螺旋态。

Non-technical description: Semiconductor heterostructures play an important role in many scientific discoveries and technological advances. While the majority of research has focused on planar heterostructures, non-planar heterostructures, particularly nanowires, have recently gained significant interest. This research project addresses fundamental questions regarding the processing and characterization of non-planar semiconductor heterostructures, particularly silicon-germanium core-shell nanowires. The research activities are designed to advance knowledge in materials synthesis and characterization, and thus assist in the design of future high-speed, low-power electronic devices. The research activities are well integrated with students education and training in cutting-edge research. More specifically, this effort educates graduate and undergraduate students in semiconductor growth, fabrication and characterization techniques, and the research results are integrated into course material and outreach lectures to high-school students to encourage careers in science, technology, and engineering. Technical Description: Semiconductor nanowires provide a versatile platform to realize epitaxial, non-planar heterostructures, with relevance for fundamental science and technological applications. The main objectives of this research project are (1) to advance the growth of group IV nanowire heterostructures by combining band engineering and modulation doping, (2) to characterize their structural and electronic properties and (3) to realize and explore quantum confined electron systems in coherently strained Si-SiGe core-shell nanowires. More specifically, these nanowire heterostructures are grown pseudomorphic using a combination of the vapor-liquid-solid growth for the Si nanowire core, and the ultra-high-vacuum chemical vapor deposition for epitaxial SiGe shell. The strain distribution in Si-Ge core-shell nanowires is experimentally probed using micro Raman spectroscopy coupled with lattice dynamic theory, and compared with calculations. Nanowire heterostructures-based field-effect transistors with low resistance contacts are fabricated and characterized under low temperatures, in order to determine the electron mobility and correlate it with the nanowire heterostructure design. Band engineering and radial modulation doping are combined to enhance the mobility of one-dimensional electrons in Si-SiGe core-shell nanowires. Using self-consistent density simulations and the experimental nanowire conductance dependence on density, the band offset between the core and the shell in Si-SiGe core-shell nanowires is extracted. The magnetotransport properties of high mobility one-dimensional hole system in Ge-SiGe core-shell nanowires are investigated experimentally, with an emphasis on spin splitting and spin-orbit interaction in order to assess if helical states with the aligned spin and momentum can be experimentally observed.