Modelling of Quantum Transport in Nanostructures

Research output: ThesisDoctoral Thesis (compilation)

Abstract

In this thesis, theoretical studies of the transport properties of three nanoscale systems: one-dimensional (1D) quantum wires (QWRs), zero-dimensional (0D), laterally confined, double-barrier resonant tunnelling structures (DBRTSs) and three-terminal ballistic junctions (TBJs), have been performed. In the first part of the thesis, an overview of the realization and properties of such systems is given along with a description of modelling tools used in the calculations. The second and main part of the thesis contains the original research results, summarized into seven papers.

The conductance of QWRs with corrugated boundaries is investigated in Paper I with respect to the nature of the boundary roughness, geometrical parameters of the QWR and temperature. It is shown that, due to the structural imperfections, the conductance exhibits rapid fluctuations, strong, broad dips between adjacent conductance plateaus at very low temperatures and, in general, a suppression of the conductance below the values expected for an ideal QWR. The results agree with existing experimental results.

Experimental studies of the transport properties of 0D quantum dots obtained by laterally confining vertical DBRTSs by means of metallic gates have shown complex, gate-dependent fine structure in the measured current-voltage (I-V) characteristics. The origin of this fine structure is theoretically studied and explained (Papers II-V) in terms of quasi-1D-0D-1D systems with a tunable lateral confinement. It is shown that, due to the low dimensionality of the emitter, dot and collector regions, complex fine structure, which is strongly dependent on Fermi energy, source-drain voltage, and gate voltage, is formed in the I-V characteristics, which may explain the experimentally observed results. A tentative comparison between experiments and theory is made in Paper IV.

Three-terminal junction systems have very recently emerged as excellent candidates for use as building blocks in the formation of nanoscale electronic devices. A general formalism for the calculation of electron transport through three- terminal quantum structures is presented in Paper VI. Using this method, the transport through Y-shaped TBJ structures is studied in Paper VII. Quantum effects are shown to influence the transport properties of TBJs at low temperatures, possibly enabling new device functionality.

Details

Authors
  • Dan Csontos
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Condensed Matter Physics

Keywords

  • ballistic transport, quantum wire, quantum dot, resonant tunnelling, three-terminal, disorder, Physics, Fysik, Fysicumarkivet A:2002:Csontos, scattering matrix, quantum transport
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2002 Nov 29
Publisher
  • Division of Solid State Physics, Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden,
Print ISBNs91-628-5460-7
Publication statusPublished - 2002
Publication categoryResearch

Bibliographic note

Defence details Date: 2002-11-29 Time: 13:15 Place: Lecture Hall B, Department of Physics, Lund University External reviewer(s) Name: Büttiker, Markus Title: Prof Affiliation: Département de Physique Théorique, Université de Genève --- Article: Effects of boundary roughness on the conductance of quantum wiresDan Csontos and Hongqi XuApplied Physics Letters 77, 2364 (2000). Article: Transmission and I-V characteristics of laterally-confined resonant tunneling structuresDan Csontos and Hongqi XuMicroelectronic Engineering 51-52, 201 (2000). Article: Physical origins of fine structure in the resonant tunneling through laterally confined 1D-0D-1D structuresDan Csontos and Hongqi XuJapanese Journal of Applied Physics 40, 1966 (2001). Article: Coupling between lateral modes in a vertical resonant tunneling structureBoel Gustafson, Dan Csontos, Michihiko Suhara, Lars-Erik Wernersson, Werner Seifert, Hongqi Xu, and Lars SamuelsonPhysica E 13, 950 (2002). Article: Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentialsDan Csontos and Hongqi XuAccepted for publication in Physical Review B. Article: Scattering-matrix formalism of electron transport through three-terminal quantum structures: Formulation and application to Y-junction devicesDan Csontos and Hongqi XuAccepted for publication in Journal of Physics: Condensed Matter. Article: Quantum effects in the transport properties of nanoelectronic, three-terminal Y-junction devicesDan Csontos and Hongqi XuTo be submitted to Physical Review B.