Conybeare, Rebecca Louise;
(2025)
Towards atomic-scale quantum structure fabrication in germanium.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
STM nanofabrication of single- and few-atom quantum devices in silicon, using a scanning tunnelling microscope (STM) to place dopant atoms with atomic precision, is a well-established technique which has been used to fabricate devices such as the single-atom transistor and two-qubit gates. However, scaling up to large numbers of dopants is difficult, so other material combinations are being explored. This thesis explores the use of germanium as an alternative substrate to silicon, with results providing strong evidence that atomically-precise arsenic devices in germanium could surpass devices in silicon in placement accuracy and overall device performance. This is motivated by recent work which showed that, unlike any previously studied dopant/precursor system, arsenic on Ge(001) incorporates at room temperature. I present STM and angle-resolved photoemission spectroscopy (ARPES) measurements of two-dimensional arsenic δ-layers. This is the first time that the band structure of δ-doped germanium has been experimentally determined. I show that the donor electrons are better confined in the out-of-plane direction than equivalent silicon samples. The characteristics of hydrogen-terminated Ge(001) are investigated. This is an important surface to fully understand before successful in-plane confinement of dopant atoms and future device fabrication. I identify several defects which are previously unseen on Ge(001), including a dimer phase defect which has never been previously observed on Ge(001) or Si(001). One-dimensional and zero-dimensional confinement of arsenic atoms on Ge(001) is demonstrated using STM hydrogen lithography. This is the first time that single-atom placement of any dopant has been achieved on Ge(001) and the first time that a single dopant atom has been incorporated at room temperature for any substrate. Achieving 2D, 1D, and 0D confinement of arsenic atoms in Ge(001) demonstrates that excellent placement accuracy is possible while showing fundamental advantages over silicon. Together, these results represent a significant step towards STM-fabricated quantum devices in germanium.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Towards atomic-scale quantum structure fabrication in germanium |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10210499 |
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