Quantum dot spectroscopy by single-electron pumping

E-114: T. Wenz:
Quantum dot spectroscopy by single-electron pumping
160 S., 79 Abb., ISBN 978-3-95606-439-5, 2018 € 20,00
Quantum dots in semiconductor nanostructures are small islands that can capture individual
electrons. They are building blocks for many very active research topics, suchas quantum computers and experiments on electron quantum optics. Another important application are single-electron pumps, which enable a representation of the SI-unit ampere by transporting a well known number of electrons with a certain repetition frequency. For many applications, detailed knowledge of the quantum dot properties is necessary. Using established methods, it is not always possible to access all features of a quantum dot. In this work, methods for quantum dot spectroscopy using the principle of single-electron pumping are presented and evaluated for samples based on the material systems silicon and GaAs.

In silicon nanostructures, individual dopant atoms can form natural quantum dots
with strongly localized potential wells. In this work, the coupling of a metallic quantum
dot to the leads is controlled by dopant atoms. With this structure, a protocolfor single-electron pumping is introduced and examined. Its suitability for metrology applications is evaluated. Furthermore, pumping measurements enable investigation of the electrostatics in a region where conventional characterization fails.

GaAs-based tunable-barrier single-electron pumps are considered to be the most
promising candidates for metrology applications. In this work, the dynamic loading of
electrons into the quantum dot is studied close to the Fermi edge. The measurementsare analyzed using a rate-equation model and reveal the inner structure of the quantum
dot. It is shown that loading into excited orbital states and subsequent fast orbital
relaxation is vital for single-electron capture. For the loading of electron pairs, no
relaxation is observed between specific states, which is attributed to the slow timescales
of singlet-triplet spin relaxation.