Bragg, Jamie S;
(2025)
Characterisation of atomically thin arsenic layers and wires in silicon.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The atomic-precision placement of dopant atoms in silicon with a scanning tunnelling microscope could greatly advance both classical and quantum computing. The list of dopants compatible with this method has recently expanded from just phosphorus to include arsenic and boron. Arsenic is especially promising for single-atom devices like qubits, because a single arsenic atom can be reliably placed. This thesis aims to characterise arsenic layers and wires in silicon, to assess their suitability for devices. A review is presented on the state of the art in the dopant placement process and the resulting devices. Then techniques to characterise dopant devices are reviewed, followed by results from these techniques to assess the impact of dopant species on device performance. The first piece of original work addresses the lack of techniques to non-destructively characterise the location of buried dopants. X-ray fluorescence and reflectometry are used to non-destructively measure the lateral and vertical distribution of dopant layers. The X-ray reflectometry results demonstrate that arsenic layers in silicon can be made with sub-nanometre thicknesses. Secondly, the thickness of the electron distribution in arsenic and phosphorus layers is characterised by measuring their conductivity as a function of magnetic field (magnetoconductivity). Previously, this method was unsuitable for arsenic layers due to an unknown negative magnetoconductivity contribution. The origin of this contribution is found to be the influence of the Zeeman effect on electron-electron interactions. This can be subtracted, allowing electronic thicknesses to be extracted for arsenic layers. These match the sub-nanometre physical thickness from X-ray reflectometry. Finally, the electrical characterisation methods for dopant layers are adapted to nanoscale arsenic wires made with a scanning tunnelling microscope. The wires are found to have conductivities, electron densities, and thicknesses comparable to those of micron-scale layers. This demonstrates that arsenic nanowires are suitable for use in quantum devices.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Characterisation of atomically thin arsenic layers and wires in silicon |
| 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 Engineering Science > Dept of Electronic and Electrical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10215494 |
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