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LUND UNIVERSITY LIBRARIES

Thermoelectric measurements on InAs nanowires with a ratchet-barrier

Lundström, Hanna LU (2022) PHYM01 20212
Department of Physics
Solid State Physics
Abstract
Efficient extraction of thermal energy from electrons at the micro- and nanoscale
is a long-standing scientific goal that could enable novel types of heat engines,
heat management, and solar cell applications. Semiconductor nanowires are
a promising system for investigating such devices for several reasons, such as
their thermoelectric properties, and the potential to be grown in heterostructures with high flexibility. This provides great potential to tune the nanowire
properties to suit specific applications, for example to generate band structures
that act as filters to extract charge carriers with specific energies. Such energy
filters have previously been investigated in nanowires, including rectangular
thermionic barriers and... (More)
Efficient extraction of thermal energy from electrons at the micro- and nanoscale
is a long-standing scientific goal that could enable novel types of heat engines,
heat management, and solar cell applications. Semiconductor nanowires are
a promising system for investigating such devices for several reasons, such as
their thermoelectric properties, and the potential to be grown in heterostructures with high flexibility. This provides great potential to tune the nanowire
properties to suit specific applications, for example to generate band structures
that act as filters to extract charge carriers with specific energies. Such energy
filters have previously been investigated in nanowires, including rectangular
thermionic barriers and quantum dots, but have been limited in either conversion efficiencies or power output. It is therefore of interest to investigate other
systems to function as energy filters. For example, the influence of the shape
of a thermionic barrier on thermionic current extraction has not been explored
in-depth. In order to expand the understanding of how to most effectively
extract energy from energetic electrons, this master thesis aims to investigate
whether an asymmetrically shaped thermionic barrier leads to an asymmetric
thermoelectric response. For this purpose, thermoelectric measurements have
been performed on indium arsenide (InAs) nanowires with a compositionally
graded indium arsenide phosphide (InAs(1−x)P(x)) segment, forming an asymmetrically shaped potential barrier, using a top-heater architecture for applying
temperature gradients along the nanowire. Thermoelectric currents were successfully generated as a result of a temperature gradient along the nanowire at
ambient temperatures of 77 K and 300 K. At an ambient temperature of 77 K,
asymmetric thermoelectric behaviour was demonstrated, with a generation of
higher open circuit voltage when heating on one side of the barrier compared
to heating on the other. This was proposed to be a result of the asymmetry of
the barrier, and an indication that the shape of the barrier matters thermionic
current extraction. The experimentally obtained results were compared to a
theoretical model based on the WKB approximation, which captured some of
the key features of the experimental results. At an ambient temperature below
1 K, indications quantum dot formation could be seen, further complicating
the thermoelectric characterization and therefore such measurements were not
further pursued. (Less)
Please use this url to cite or link to this publication:
author
Lundström, Hanna LU
supervisor
organization
course
PHYM01 20212
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
9078514
date added to LUP
2022-04-25 16:31:11
date last changed
2022-04-25 16:31:11
@misc{9078514,
  abstract     = {{Efficient extraction of thermal energy from electrons at the micro- and nanoscale
is a long-standing scientific goal that could enable novel types of heat engines,
heat management, and solar cell applications. Semiconductor nanowires are
a promising system for investigating such devices for several reasons, such as
their thermoelectric properties, and the potential to be grown in heterostructures with high flexibility. This provides great potential to tune the nanowire
properties to suit specific applications, for example to generate band structures
that act as filters to extract charge carriers with specific energies. Such energy
filters have previously been investigated in nanowires, including rectangular
thermionic barriers and quantum dots, but have been limited in either conversion efficiencies or power output. It is therefore of interest to investigate other
systems to function as energy filters. For example, the influence of the shape
of a thermionic barrier on thermionic current extraction has not been explored
in-depth. In order to expand the understanding of how to most effectively
extract energy from energetic electrons, this master thesis aims to investigate
whether an asymmetrically shaped thermionic barrier leads to an asymmetric
thermoelectric response. For this purpose, thermoelectric measurements have
been performed on indium arsenide (InAs) nanowires with a compositionally
graded indium arsenide phosphide (InAs(1−x)P(x)) segment, forming an asymmetrically shaped potential barrier, using a top-heater architecture for applying
temperature gradients along the nanowire. Thermoelectric currents were successfully generated as a result of a temperature gradient along the nanowire at
ambient temperatures of 77 K and 300 K. At an ambient temperature of 77 K,
asymmetric thermoelectric behaviour was demonstrated, with a generation of
higher open circuit voltage when heating on one side of the barrier compared
to heating on the other. This was proposed to be a result of the asymmetry of
the barrier, and an indication that the shape of the barrier matters thermionic
current extraction. The experimentally obtained results were compared to a
theoretical model based on the WKB approximation, which captured some of
the key features of the experimental results. At an ambient temperature below
1 K, indications quantum dot formation could be seen, further complicating
the thermoelectric characterization and therefore such measurements were not
further pursued.}},
  author       = {{Lundström, Hanna}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Thermoelectric measurements on InAs nanowires with a ratchet-barrier}},
  year         = {{2022}},
}