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Title: Bound exciton-assisted spin-to-charge conversion of donors in silicon
Author: Ross, M. P.
ISNI:       0000 0004 7225 4560
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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Donor spins in silicon are promising candidates for quantum information applications. The information storage time in donor qubits greatly exceeds the single operation time-scale and hence promises fast and accurate quantum computation, as well as highly sensitive magnetometers. Yet, the spin-readout of single donors and small donor ensembles remains non-trivial. One potential spin-to-charge conversion method is provided by the bound exciton, which is a long-lived, excited state of the donor that can be created optically in a spin-selective manner. It decays via an Auger process, whereby the donor is ionized while the electron is promoted to the conduction band, resulting in a spin-dependent change of sample conductivity. The main subject of this thesis is to understand the physical processes surrounding the photoconductivity of the bound exciton transition and to take first steps towards the spin-measurement of small donor ensembles in devices. To this end, first, fundamental properties of the bound exciton transition are studied. Expressions for the transition energy-dependence to strain and magnetic fields are derived and experimentally validated. Furthermore, a proper treatment of the competing processes of direct, spin-independent donor ionisation is introduced, which significantly impacts the achievable read-out fidelity and spin polarisation. Secondly, experiments utilizing the bound exciton transition for spin resonance experiments on bulk samples are presented. After a development of a circuit-model for the capacitive measurement technique, coherence time measurement of the phosphorus electron spin in highly purified silicon-28 samples are presented and a novel, electrical method for state tomography of donor ensembles is developed. Lastly, usage of the bound exciton transition in silicon devices is demonstrated with spin resonance measurements showing the potential for device-based magnetometry. Thereafter, a multitude of transport processes for n-type silicon at 4K and under illumination are found and explained using current-voltage measurements. Finally, the relatively small sensitivity of the bound exciton transition energy to electric fields is determined.
Supervisor: Morton, J. J. L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available