Abstract
This thesis experimentally investigates the possibilities of using quantum effects in semiconductor nanostructures for engineering their thermoelectric properties. More specifically, heterostructured InAs/InP nanowires are used to create short InAs quantum dots (QDs) with electronic state structure resembling that found in atoms. Recently developed topheater architecture is used to apply a temperature differential across the QDs. The nanowirebased QD devices are used for studies of thermoelectric effects at the nanoscale and for experimental demonstration of particleexchange heat engines.
This thesis first gives an overview of the most important physical effects governing the behavior of quantum dots (QDs). The Master equation approach to model the electronic transport in QDs is introduced in the sequential electron tunneling approximation. It is used to illustrative the transport behavior of QDs. The LandauerBüttiker approach is also introduced as a reference and the differences with the sequential electron tunneling approximation are discussed. A summary of the most important literature on the thermoelectric properties of single QDs is given and discussed to provide the context for the experimental studies in this thesis. Finally, a description of the experimental methods used in this thesis is given.
There are three studies included in this thesis. The first investigates the nonlinear thermoelectric response of a QD with an applied thermal bias. A strongly nonlinear behavior is observed which can be fully explained by the interplay between different QD electronic states contributing to thermocurrent in opposing directions. The second study experimentally demonstrates efficient particleexchange heat engines based on QDs for the first time. The analysis of the heat engines' power and efficiency indicate heattoelectric conversion efficiencies up to 70% of Carnot efficiency. The third study investigates the thermoelectric response of QDs in the presence of Kondo correlations. It verifies a previous theoretical prediction that the sign of the thermoelectric signature in QDs inverts due to the Kondo correlations.
The experiments presented in this thesis have been successful in filling a gap between theory and experiments on several fronts. Future experiments could, for example, study Kondocorrelated QDs in the nonlinear thermoelectric response regime in the presence of magnetic field, where theory predictions are harder to obtain, or could employ thermoelectric characterization techniques to study entropy of various different QD states.
This thesis first gives an overview of the most important physical effects governing the behavior of quantum dots (QDs). The Master equation approach to model the electronic transport in QDs is introduced in the sequential electron tunneling approximation. It is used to illustrative the transport behavior of QDs. The LandauerBüttiker approach is also introduced as a reference and the differences with the sequential electron tunneling approximation are discussed. A summary of the most important literature on the thermoelectric properties of single QDs is given and discussed to provide the context for the experimental studies in this thesis. Finally, a description of the experimental methods used in this thesis is given.
There are three studies included in this thesis. The first investigates the nonlinear thermoelectric response of a QD with an applied thermal bias. A strongly nonlinear behavior is observed which can be fully explained by the interplay between different QD electronic states contributing to thermocurrent in opposing directions. The second study experimentally demonstrates efficient particleexchange heat engines based on QDs for the first time. The analysis of the heat engines' power and efficiency indicate heattoelectric conversion efficiencies up to 70% of Carnot efficiency. The third study investigates the thermoelectric response of QDs in the presence of Kondo correlations. It verifies a previous theoretical prediction that the sign of the thermoelectric signature in QDs inverts due to the Kondo correlations.
The experiments presented in this thesis have been successful in filling a gap between theory and experiments on several fronts. Future experiments could, for example, study Kondocorrelated QDs in the nonlinear thermoelectric response regime in the presence of magnetic field, where theory predictions are harder to obtain, or could employ thermoelectric characterization techniques to study entropy of various different QD states.
Original language  English 

Qualification  Doctor 
Awarding Institution 

Supervisors/Advisors 

Award date  2018 Oct 12 
Place of Publication  Lund 
Publisher  
ISBN (Print)  9789177538325 
ISBN (electronic)  9789177538332 
Publication status  Published  2018 
Bibliographical note
Defence detailsDate: 20181012
Time: 09:15
Place: Rydbergsalen, Fysicum, Professorsgatan 1, Lund University, Faculty of Engineering LTH.
External reviewer(s)
Name: Ensslin, Klaus
Title: Professor
Affiliation: ETH Zürich, Zürich, Switzerland

Subject classification (UKÄ)
 Nano Technology
Keywords
 Quantum dots
 Nanowire
 Thermoelectric
 Maximum power
 Efficientcy
 Carnot
 Kondo effect
 Fysicumarkivet A:2018:Svilans