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