Electron Transport in Semiconductor Nanostructures

本实验研究项目探讨了电子在隧道耦合量子点中的行为。打个恰当的比方，这样的系统可以被看作是人造分子，单个的点被看作是原子。这些系统中电子的基本特性；电子如何在点之间共享，共享电子态的能量，以及电子如何在耦合点电路中移动；都很有趣。具体测量包括小隧道耦合点（每个点少于100个电子）的库仑封锁光谱；量子霍尔区隧道耦合点的库仑封锁谱部分开放导联的单量子点传输，预计会显示有趣的多体效应；以及通过开放电子波谐振器的传输。Dot样品是在哈佛大学利用电子束光刻技术在加州大学圣巴巴拉分校通过分子束外延生长的GaAs/AlGaAs晶圆上制作的。该研究项目是跨学科的，涉及一名或多名研究生，他们接受了优秀的培训，为工业、政府实验室或学术界的职业生涯做准备。本实验研究计划探讨在量子机械电子隧穿耦合下半导体量子点中电子的行为。打个恰当的比方，这样的系统可以被看作是人造分子，单个的点被看作是原子。“量子点”是GaAs/AlGaAs晶圆表面的一个小区域，类似于先进微电子设备中使用的区域。在整个晶圆片表面下产生二维电子气体，然后使用电子束光刻技术沉积微型电极，这种技术可以分离出含有100个电子的微小区域，称为量子点。这些系统中电子的基本特性；电子如何在点之间共享，共享电子状态的能量，以及电子如何在耦合点电路中移动，都是令人感兴趣的。具体测量包括小隧道耦合点（每个点少于100个电子）的库仑封锁光谱；量子霍尔区隧道耦合点的库仑封锁谱部分开放导联的单量子点传输，预计会显示有趣的多体效应；以及通过开放电子波谐振器的传输。Dot样品是在哈佛大学利用电子束光刻技术在加州大学圣巴巴拉分校通过分子束外延生长的GaAs/AlGaAs晶圆上制作的。这项研究与未来电子器件接近大分子大小有关。在这种尺度下，即使在室温下，量子力学也很重要。量子现象为计算提供了新的方法，从超密单电子存储器到量子计算机，预计将使速度呈指数级增长。这里的研究解决了隧道耦合半导体纳米结构中量子力学电子态和电子传输的基本特征，作为迈向这些可能应用的第一步。该研究项目是跨学科的，涉及一名或多名研究生，他们接受了优秀的培训，为工业、政府实验室或学术界的职业生涯做准备。＊＊＊

w:\awards\awards96\*.doc 9802242 Westervelt This experimental research project investigates the behavior of electrons in tunnel-coupled quantum dots. In an apt analogy, such systems can be regarded as artificial molecules, the individual dots being considered as atoms. The fundamental characteristics of electrons in these systems; how electrons are shared between dots, the energy of shared electron states, and how electrons move through coupled dot circuits; are of interest. Specific measurements include Coulomb blockade spectroscopy of small tunnel-coupled dots (less than 100 electrons per dot); Coulomb blockade spectroscopy of tunnel-coupled dots in the quantum Hall regime; transport through single quantum dots with partially open leads, predicted to show interesting many body effects; and transport through open electron wave resonators. Dot samples are made at Harvard using electron beam lithography on GaAs/AlGaAs wafers grown via molecular beam epitaxy at Univ. California Santa Barbara. This research program is interdisciplinary in nature and involves one or more graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project investigates the behavior of electrons in semiconductor quantum dots coupled by quantum- mechanical electron tunneling. In an apt analogy, such systems can be regarded as artificial molecules, the individual dots being considered as atoms. The "quantum dot" is a small region in the surface of a GaAs/AlGaAs wafer, similar to those used in advanced microelectronic devices. A two-dimensional electron gas is produced just below the surface of the entire wafer, and then miniature electrodes are deposited using electron beam lithography which can isolate a tiny region containing as few as 100 electrons, called a qu antum dot. The fundamental characteristics of electrons in these systems; how electrons are shared between dots, the energy of shared electron states, and how electrons move through coupled dot circuits, are of interest. Specific measurements include Coulomb blockade spectroscopy of small tunnel-coupled dots (less than 100 electrons per dot); Coulomb blockade spectroscopy of tunnel-coupled dots in the quantum Hall regime; transport through single quantum dots with partially open leads, predicted to show interesting many body effects; and transport through open electron wave resonators. Dot samples are made at Harvard using electron beam lithography on GaAs/AlGaAs wafers grown via molecular beam epitaxy at Univ. California Santa Barbara. The research is relevant to future electronics in which devices will approach the size of large molecules. At this size scale quantum mechanics is important even at room temperature. Quantum phenomena offer new approaches to computation ranging from ultra dense single-electron memories to quantum computers projected to give an exponential increase in speed. The research here addresses the fundamental characteristics of quantum mechanical electron states and electron transport in tunnel-coupled semiconductor nanostructures as a first step toward these possible applications. This research program is interdisciplinary in nature and involves one or more graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***