Electrical readout of orbital state transitions from fewer hydrogenic donors in silicon
Creators: name: Stockbridge, Kristian
Publisher: name: University of Surrey
Year: 2024

description: Atomic defects in semiconductors have been studied as promising platforms for quan-
description: tum technological applications in the solid state. The electron and nuclear spins of
description: single substitutional group-V donor atoms in silicon are of particular interest due to
description: their long quantum coherence times and potential ease of integration with already
description: well established microelectronics fabrication technology. The donor electrons, when
description: bound to group-V donor nuclei at low temperature, have not only quantised intrin-
description: sic spin but quantised orbital angular momentum. For donors in silicon, transitions
description: between the allowed orbital states are accessible via THz excitation and the extent
description: of the excited orbital wave function is large inspiring their use to gate interaction be-
description: tween neighbouring spin qubits. This body of work seeks to investigate the electrical
description: detection of the orbital excitation dynamics of scaled down silicon devices whereby
description: orbital excitation is of few defects.<br>
description: <br>
description: Prior to fabrication of electrical devices that will require deterministic and precise
description: placement of single donor atoms, it is worth checking that gated qubit interactions
description: can’t be realised in a system that might be far easier to fabricate e.g. one where
description: dopants exist homogeneously in the bulk or are broad area ion implanted. A partic-
description: ular gating scheme whereby qubit entanglement is dependant on the orbital state of
description: an intermediary donor has been proposed historically. In this thesis the viability of
description: an even simpler system of orbitally gated interaction being achieved by a number of
description: broad area ion implantations is investigated using point process statistics and the
description: need for higher positional determinism in dopant placement realised.<br>
description: <br>
description: The next investigation is of isolated donors present at a background concentra-
description: tion level in highly purified silicon wafer. Though not deterministically placed, the
description: quantum coherence dynamics of these donors can be probed electrically via contact-
description: less photocurrent detection. The coherent dynamics of the donor ensemble subjected
description: to a large external magnetic field was measured using Ramsey spectroscopy. Ex-
description: ternal magnetic fields are typically used in spin qubit systems to lift the energy
description: degeneracy of spin-up and spin-down states of the electron.<br>
description: <br>
description: Finally, resistive photoconductance spectroscopy was performed on a bismuth
description: ion implanted silicon-on-insulator (SOI) device containing &lt;1 million defects in the
description: optically active region of the device. The high electric fields that are more eas-
description: ily accessible in short channel devices is shown to introduce additional ionisation
description: mechanisms that could aid in characterising donor orbital state transition dynam-
description: ics at lower temperatures. The significant inhomogeneous broadening seen in the
description: measured device photocurrent spectrum was attributed to the high density of active
description: bismuth donors.<br>