Bismuth implantation and fabrication routes towards silicon donor based quantum technologies.

Abstract

Group V donors in silicon are extremely promising candidates for applications within quantum technologies due to their long spin coherence lifetimes and existing compatibility within the microelectronics industry. However, there are various technical challenges which need to be overcome in order to achieve this potential. This body of work aims to address two such fabrication challenges and attempt to provide solutions which will aid the realisation of silicon and donor based quantum architectures. Bismuth donors display a vast potential for the implementation as spin qubits however there are limited techniques to controllably fabricate a high quality Si:Bi doped system. Ion implantation is the leading candidate to achieve this although there are concerns that the violent mechanism of Bi+ bombardment into the silicon lattice will significantly degrade the condition of the crystal environment. Therefore, the formation of bismuth donor states in silicon using ion implantation is studied with a specific emphasis on the quality of dopant incorporation. Using a combination of electrical measurements and donor bound exciton spectroscopy it is determined that, under the appropriate annealing conditions, it is possible to produce ion implanted bismuth donors in an environment free from the effects of lattice strain. This therefore motivates the use of ion implanted samples as an alternative to bulk doped Si:Bi for applications within quantum technologies. Implanted samples are then fabricated into simple two terminal devices and used in electrically detected THz spectroscopy measurements. Using a free electron laser, the resonant excitation of implanted bismuth donors is observed, however the characteristic properties of photoconductivity spectra strongly suggest that devices are being heated significantly. Finally, an alternative to bulk silicon is studied as a vehicle for quantum technologies. Specifically, the fabrication requirements to controllably align single crystal silicon nanowires is studied using a process known as dielectrophoresis, DEP. Here it is demonstrated that, under the appropriate experimental conditions, it is possible to utilise DEP to manipulate single silicon nanowires to fabricate a wide range of devices. This could prove highly beneficial for the integration of this material within quantum technologies.