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Chemistry and structural properties of adsorbates on germanium for optoelectronics and quantum computing

Hofmann, Emily Victoria Stone; (2022) Chemistry and structural properties of adsorbates on germanium for optoelectronics and quantum computing. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

In recent years, the prominence of germanium (Ge) in complementary metal-oxide-semiconductor (CMOS) technology has steadily increased, expanding into novel fields, such as optoelectronics and quantum computing. Germanium-tin (GeSn) alloys are strong contenders for laser integration into the CMOS platform, and atomic scale precision single dopant placement of arsenic (As) via arsine (AsH₃) dosing is an interesting avenue for dopant qubit fabrication in Ge. This work uses scanning tunnelling microscopy (STM) to explore the surface chemistry and structural properties of Sn layer growth on, and AsH₃ dosing of, Ge. First, I detail the formation of a high Sn content GeSn wetting layer on Ge(100) at room temperature. I demonstrate that Sn incorporation leads to Ge presence in the three ad-features and show the ad-features tile the surface to form a wetting layer as well as the formation of a second Sn monolayer. Moreover, annealing sub- and full monolayer Sn coverages leads to surface reconstruction and, at sub-monolayers, full Sn incorporation. I obtain insight into Sn bilayer formation on Ge(111) at room temperature and ~ 200 K. I demonstrate Sn incorporation and the formation of a disordered wetting (bi)layer at either growth temperature. Annealing sub-bilayer Sn coverages gives full incorporation. Furthermore, annealing a full Sn bilayer produces two surface phases: phase A without long-range order and, at 300°C, phase B with long range order, for which I suggest possible structure models. I demonstrate the potential of AsH₃ as a precursor for atomic scale placement of As using STM hydrogen resist lithography on Ge(100). I identify nine AsH₃ dissociation products at room temperature. By annealing, I achieve full AsH₃ dissociation and As incorporation in the Ge surface, with hydrogen desorption thereafter. Finally, I show that the heavily As doped surface can be capped by Ge, with As remaining in place in the growth direction.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Chemistry and structural properties of adsorbates on germanium for optoelectronics and quantum computing
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2022. 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 > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10142608
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