Tunnel-Coupled Quantum Dots: Atomistic Theory of Quantum Dot Molecules and Arrays
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Tunnel-Coupled Quantum Dots: Atomistic Theory of Quantum Dot Molecules and Arrays Garnett W. Bryant1, Javier Aizpurua1, W. Jaskolski2 and Michal Zielinski2 1 Atomic Physics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8423 2 Instytut Fizyki, UMK, Grudziadzka 5, 87-100 Torun, Poland
ABSTRACT An understanding of how dots couple in quantum dot molecules and arrays is needed so that the possibilities for tailored nanooptics in these systems can be explored. The properties of tunnel-coupled dots will be determined by how the dots couple through atomic-scale junctions. We present an atomistic empirical tight-binding theory of coupled, CdS nanocrystal artificialmolecules, vertically and laterally coupled InAs/GaAs self-assembled dots, and arrays of InAs/GaAs self-assembled dots. Electron states follow the artificial molecule analogy. The coupling of hole states is much more complex. There are significant departures from the artificial molecule analogy because the interdot hole coupling is determined by the hole envelope functions, as for the electron states, and by the hole atomic state near interdot interfaces.
INTRODUCTION Quantum dots and nanocrystals have been studied intensely due to their enticing possibilities as artificial atoms with enhanced optical properties. It is now possible to envision using these artificial atoms as the building blocks for novel artificial solids or as the device elements in complex nanoarchitectures. Artificial solids could be constructed from dots without the limitations on geometry and composition normally imposed by chemical bonding in natural solids. Nanoarchitectures of dots provide the possibility of pushing classical computing almost to the atomic regime, providing coherent quantum structures needed for quantum computing, and bridging the interface to biological systems with bio/nanohybrids. Construction of artificial solids, nanoarchitectures and bio/nanohybrids is a challenging, ongoing problem. Ensembles of quantum dots and nanocrystals ordered in one, two, and three dimensions are being studied [1-5]. An understanding of how dots should couple and function in these structures is needed so that the possibilities for tailored nanooptics in these systems can be explored. The properties of tunnel-coupled quantum dots will be determined by how the dots couple through atomic-scale tunnel junctions. Here we present an atomistic empirical tight-binding theory of coupled, CdS nanocrystal artificial-molecules, vertically and laterally coupled InAs/GaAs self-assembled dots, and one-dimensional and two-dimensional arrays of InAs/GaAs self-assembled dots.
THEORY Electron and hole states in these nanoparticle nanosystems are calculated by use of the
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empirical tight-binding (ETB) method [6-12]. The ETB approach is an atomistic approach well suited for calculating the electronic states of nanosystems with atomic-scale interfaces and variations in composition and shape. Our ETB theory can be used to model single dots or coupled dot systems
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