Quantum and Ballistic Nanodevices

University dissertation from Division of Solid State Physics, Lund University, Box 118, SE-221 00 Lund, Sweden

Abstract: In this thesis, electron transport in quantum and ballistic devices was studied. The devices studied here were quantum wires, planar quantum dots, ballistic rectifiers, artificial functional materials, and three-terminal ballistic junctions. The possible application of such devices in the future nanoelectronics was also investigated. In an electron waveguide, with an abrupt change in the geometry at the entrance and the exit, conductance oscillations, superimposed on conventional conductance plateaus, were observed. These oscillations were attributed to formation of longitudinal, resonant electron states in the waveguide, in analogy with optical Fabry-Perot effects. The Coulomb charging effects and the resonant tunneling through the lowest quantized energy level of the heterostructurally defined, planar quantum dots were studied. The ballistic rectifiers were fabricated to be small enough to show ballistic effects even at room temperature. In analogy to the ballistic rectifiers, the artificial functional nanomaterial was proposed and fabricated. The ballistic rectifiers as well as the artificial nanomaterials showed functionality at room temperature and at frequencies up to at least 50 GHz. Quantum effects in the transport behavior of the nano-scale ballistic rectifiers and the artificial materials were found to be dominant at low temperatures. Nonlinear electrical properties of three-terminal ballistic junctions were investigated. Three-terminal ballistic junctions were found to show nonlinear current-voltage, and voltage-voltage characteristics tunable by voltages applied either to one of the branches of the junction or to an external capacitively-coupled gate. These nonlinear electrical properties are observable even at room temperature and are therefore interesting from an application point of view. Integrated devices, such as the frequency multipliers based on a three-terminal ballistic junction were proposed and demonstrated. The fabricated frequency multipliers showed frequency doubling and gain at room temperature.

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