Studies of coherent transport through quantum-dot arrays and weak antilocalization in indium arsenide heterostructures

Guanlong Chen, Purdue University

Abstract

Transport through quantum dots has recently been the focus of much experimental and theoretical studies, and the single quantum dot behavior, which has shown both the energy and charge quantization, are well understood. It is the purpose of this thesis to extend the studies of single quantum dots to quantum-dot arrays, which are interesting from both basic research and device application points of view. In the theoretical studies, we apply the Hubbard Hamiltonian to describe quantum-dot arrays weakly coupled to two contacts. Exact diagonalization is used to calculate the eigenstates of the arrays containing up to 6 dots and the linear response conductance is then calculated as a function of the Fermi energy. In the atomic limit the conductance peaks form two distinct groups separated by the intra-dot Coulomb repulsion, while in the band limit the peaks occur in pairs. The cross-over is studied. A finite inter-dot repulsion is found to cause interesting rearrangements in the conductance spectrum. We have also studied the experimental feasibility of fabricating the quantum-dot arrays on InAs and GaAs. The fabrication of side-wall Schottky gates by shadow evaporation is demonstrated, and novel nanofabrication opportunities on the InAs surface two-dimensional electron gases are revealed. We have also studied low temperature magnetoconductance of a AlSb/InAs/AlSb quantum well structure and observed weak antilocalization behavior. The spin-orbital field deduced from the weak antilocalization data is found to be insensitive to the photo-induced changes in the carrier density, suggesting that the interfacial-field-induced rather than the crystal-field-induced spin-splitting is the predominant cause of spin-orbital scattering. We also find a significant enhancement of spin-orbital scattering in ZnTe/InAs/AlSb structures; this enhancement is explained by the structural asymmetry and confirms the dominant role of the interfacial fields.

Degree

Ph.D.

Advisors

James, Purdue University.

Subject Area

Electrical engineering

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