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Dr Gemma R Chapman

My publications


Solotronic devices formed from group V dopants in silicon are a prospective option as a qubit system for quantum technologies. A spin-based silicon based quantum computer is highly promising with the longest qubit coherence times found to date, and an existing compatibility with the CMOS industry. The electron spin states of silicon solotronic devices are controlled through resonance absorption of microwave frequencies. Due to the small dimensions of the dopants, integration of the microwaves to ensure individual qubit addressability is a important step on the path to producing a commercial quantum computer. Within this thesis, we investigate two different pathways to potentially optimise this process. Mesoscopic interconnects could be used to deliver microwaves to individual qubits within a qubit array. Conventional metals are not suitable as the resistivity increases as the dimensions approach the atomic scale and have immature nanoscale fabrication techniques. Highly doped metallic phosphorous delta-doped monolayers in silicon could be a viable material for mesoscopic transmission lines. Si:P delta-doped nanowires can be fabricated with atomic precision and have been shown to maintain ohmic behaviour down to wire widths of 1.5nm. The microwave characterisation of Si:P delta-doped layers was completed validating that it is a suitable material for microwave propagation. The transmission parameters are extracted and matched to a circuit model and complementary electromagnetic simulations. A universal nanoscale transmission model showed that Si:P nanowires have transmission parameters equivalent to graphene nanoribbons and have optimal behaviour compared to copper nanowires below 5nm. This investigation has further reaching applications than silicon quantum technologies as conventional microelectronics also require mesoscopic interconnects as Moore's law progresses. The application of an external magnetic field modulates the electron spin splitting within a group V donor and has a linear relationship with the resonant microwave frequency under high magnetic fields. Within the literature, external magnetic fields approaching 10T are being used to optimise the operating conditions of the qubit and to simplify the experimental parameters. Knowledge of the behaviour and mechanisms of the spin lattice relaxation is unknown at these fields. Electron spin resonance in phosphorous doped silicon was demonstrated at magnetic fields between 10-14T using electrically detected donor bound exciton spectroscopy. To accompany this investigation, the first donor bound exciton spectroscopy model under the influence of magnetic field was developed and analysed.