ISBN 978-3-8439-3398-8

978-3-8439-3398-8, Reihe Physik

Christian Neumann
Isotopically-enriched 28Si heterostructures for qubit devices

110 Seiten, Dissertation Universität Regensburg (2017), Softcover, A5

Zusammenfassung / Abstract

In this study, we realize and characterize undoped isotopically enriched 28Si/SiGe heterostructrues designed for spin qubit applications. While such heterostructures are expected to significantly improve the performance of spin-based qubits their material physics is still largely unknown.

In a first step, we assess these heterostructrues with magneto-transport measurements. We develop a qualitative band structure model in order to interpret our experimental findings. Based on the band structure model and the experimental characteristics of our current heterostructures, we find that they are suitable for quantum dot and qubit applications.

In parallel to the magneto-transport characterization, we develop the fabrication process for quantum dot samples with electron beam lithography. By optimizing the process and the design we establish a high yield process. In addition we demonstrate a high precision positioning of structures.

The second step of our study is the characterization of a double quantum dot device. We show that charge sensing and an operation of the sample down to the few electron regime is possible. In addition, we find that the electric noise is reduced by two orders of magnitude compared to previous doped samples. We determine that our experiments are mainly limited by the temperature of the cryostat used for the experiments and neither by the heterostructure nor the quantum dot design.

Our results show, that both our undoped isotopically enriched 28Si/SiGe heterostructures and the quantum dot design are a priori suitable for qubit applications. Our results pave the way for experiments towards coherence time measurements and coherent manipulation of spin qubits, which are currently realized in a follow-up project.