Electron Transport in Semiconductor Nanostructures

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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. ***