Thermally and Optically Excited Electron Transport in Semiconductor Nanowires

Forskningsoutput: AvhandlingDoktorsavhandling (sammanläggning)

Abstract

This thesis explores the transport of thermally and optically excited electrons in
various nanowire structures. On one hand, electrons are thermally excited when the
temperature is nonzero, and the thermal energy help them surmount energy barriers
that are present in the material. On the other hand, when the electron distributions
at different part of the material are out-of-equilibrium due to thermal or optical
excitations, an electrical current is created, converting the thermal and optical
energy into electricity. Thus, in this thesis, the transport of thermally and optically
excited electrons is studied to extract the electronic properties of nanowire
heterostructures and to investigate the limit of energy conversion in thermoelectric
and photovoltaic devices.

First, the measurement of thermionic emission current, which is the thermally
induced electron flow over energy barriers, is used to study the electronic properties
of InAs crystal phase heterostructures. The band offset, polarization charges, and
carrier density differences between the zinc blende and wurtzite crystal phases are
investigated. In addition, quantum dot states can be formed within a wurtzite
segment or between two closely spaced wurtzite segments in an otherwise zinc
blende nanowire. The quantum dot formed between two wurtzite segments can be
further split into two parallel coupled quantum dots. Numerical simulations are used
to understand the formation and the interaction between the two quantum dots.

Secondly, the thermoelectric response of pure zinc blende InAs nanowires is
studied. At low temperatures, the quantum confinement effect can be observed, and
the electrons exhibit quasi-1D transport. Conductance quantization and Seebeck
coefficient oscillation as a function of gate voltages, characteristic of quasi-1D
system, are observed. More importantly, a theoretical limit for the power factor of
non-ballistic 1D channels is found and tested experimentally.

Finally, the transport of optically excited electrons in InAs-InP-InAs
heterostructure nanowires is studied. Electron distributions that are out-of- thermal equilibrium with, more specifically hotter than, the lattice and the environment are
created through optical excitation with photon energies significantly larger than the
band gap. An energy barrier formed by the InP segment is used to selectively extract
high energy electrons and convert their kinetic energy into electrical potential.
Nanophotonic effects including optical resonances in nanowires and localized
surface plasmon resonances in metal nanostructures are used to create a nonuniform
hot-electron distribution around the InP barrier. In particular, the hot-electrons can
be generated locally near the controlled position of the plasmonic metal
nanostructures, which facilitates an in-depth study of their transport.

Detaljer

Författare
Enheter & grupper
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Naturvetenskap
  • Teknik och teknologier

Nyckelord

Originalspråkengelska
KvalifikationDoktor
Tilldelande institution
Handledare/Biträdande handledare
Tilldelningsdatum2018 sep 12
Förlag
  • Division of Solid State Physics, Lund University, Box 118, SE-221 00 Lund, Sweden,
Tryckta ISBN978-91-7753-794-6
Elektroniska ISBN978-91-7753-795-3
StatusPublished - 2018
PublikationskategoriForskning

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