Switching Dynamics of Electric Field Domains in Semiconductor Superlattices

*非技术摘要*本项目关注半导体超晶格中电子传输的各个方面--这种结构由不同半导体材料的许多交替层组成，每层的宽度只有几个纳米。这些结构中的电流流动是高度非线性的，这导致电流对施加电压的变化的响应中的复杂开关行为。该项目的一个主要目标是了解这种开关动力学如何依赖于一些可以系统地改变的实验参数。新的测量技术和数据分析方法将在这个项目中使用，并将适用于远离各自平衡状态运行的一系列其他物理系统。这项研究将有助于理解对新兴技术发展至关重要的物理过程。它将为超晶格的非线性电学性质提供新的、基本的见解，对一系列纳米级电子结构和光电子器件(如最先进的激光和灵敏的光探测器)具有潜在的影响。研究生和本科生培训是这个项目的核心；学生将熟练掌握尖端测量和计算机模拟技术，为在工业或学术研究中从事富有成效的职业生涯做准备。这个项目的实验样品将与德国的研究人员合作制作，这将为研究生提供宝贵的教育机会。*技术摘要*本项目通过研究具有电场域和相关电流双稳的GaAs/AlAs样品，研究半导体超晶格中非线性电子输运的基本方面。对于这样的系统，对外加电压变化的瞬时响应导致的电流切换动态可能是纯粹随机的，也可能涉及复杂的确定性和随机机制的组合。该项目研究了开关动态对接触层的导电性、施加的电压脉冲的形式、样品的横截面尺寸以及外部光激励水平的依赖关系。新的测量和数据分析方法将阐明亚稳态在电流转换中所起的重要作用。亚稳态对一系列非平衡体系的动力学有很大的影响，而超晶格由于其优异的结构特征和精确的电学测量能力，为这类研究提供了理想的体系。这项研究还将为量子隧道和空间电荷动力学的相互作用提供基本的见解，对纳米级电子结构和光电子器件具有潜在的影响。研究生和本科生将接受最先进的测量和模拟技术方面的培训，为他们在工业或学术研究领域的职业生涯做好准备。该项目的实验样本将与德国的研究人员合作制作；这将为研究生提供宝贵的教育机会。

****NON-TECHNICAL ABSTRACT****This project focuses on aspects of electronic transport in semiconductor superlattices - structures that are composed of many alternating layers of different semiconductor materials, with each layer having a width of only a few nanometers. The flow of electrical current in these structures is highly nonlinear and this leads to complex switching behavior in the current response to changes in applied voltage. A major objective of the project is to understand how this switching dynamics depends on a number of experimental parameters that can be systematically varied. New measurement techniques and data analysis methods will be utilized in this project and will be applicable to a range of other physical systems that operate far from their respective equilibrium states. This research will contribute to the understanding of physical processes that are important for emerging technological development. It will provide new, fundamental insight into the nonlinear electrical properties of superlattices with potential impact for a range of nanoscale electronic structures and optoelectronic devices, such as state-of-the-art lasers and sensitive light detectors. Graduate and undergraduate training is central to this project; students will become skilled in cutting edge measurement and computer simulation techniques preparing them for productive careers in industry or academic research. Experimental samples for this project will be fabricated in collaboration with researchers in Germany, and this will provide valuable educational opportunities for graduate students.****TECHNICAL ABSTRACT****This project addresses fundamental aspects of nonlinear electronic transport in semiconductor superlattices through the investigation of GaAs/AlAs samples that possess electric field domains and associated current bistability. For such systems, the transient response to changes in applied voltage leads to current switching dynamics that may be purely stochastic or may involve a combination of complex deterministic and stochastic mechanisms. The project investigates the dependence of switching dynamics on the conductivity of contact layers, the form of applied voltage pulses, the cross sectional dimensions of samples, and the level of external photoexcitation. Novel measurement and data analysis methods will elucidate the important role played by metastable states in current switching. Metastable states strongly influence dynamics for a wide range of non-equilibrium systems, and superlattices offer an ideal system for such studies due to their excellent structural characterization and capability for precise electrical measurement. This research will also provide fundamental insight on the interplay of quantum tunneling and space-charge dynamics, with potential impact for nanoscale electronic structures and optoelectronic devices. Graduate and undergraduate students will be trained in state-of-the-art measurement and simulation techniques providing them with strong preparation for careers in industry or academic research. Experimental samples for this project will be fabricated in collaboration with researchers in Germany; this will provide valuable educational opportunities for graduate students.