Comparison of dopant species for atomically-precise devices in silicon

A process has been developed to position individual dopant atoms in precise locations in silicon. This technique may have applications in making new electronic devices such as quantum computers.
The list of dopants compatible with this process has recently expanded from just phosphorous to include arsenic and boron. This PhD project aims to understand how the different properties of these dopants can be best employed for devices, in particular comparing phosphorous and arsenic.
The actual work involves making dopant atom structures using scanning tunnelling microscopy, and then connecting them to macroscopic wires using cleanroom techniques such as electron beam lithography and reactive ion etching.
Using this method, thin sheets of phosphorous and arsenic have been made and measured electrically at low temperature in a magnetic field. Under certain conditions, the conductivity decreases with magnetic field, the opposite trend to that seen in previous experiments. Comparing the data to theory suggests that this is caused by electron-electron interactions. A method has been developed to extract the thickness of the sheet from this data.
The remainder of the project will involve the fabrication and electrical measurement of nanoscale wires made of both phosphorous and arsenic, and dopant devices on insulating layers which allow control of the electron density in the device.

The production and processing of materials accounts for 15% of UK GDP and generates exports valued at £50bn annually, with UK materials related industries having a turnover of £197bn/year. It is, therefore, clear that the success of the UK economy is linked to the success of high value materials manufacturing, spanning a broad range of industrial sectors. In order to remain competitive and innovate in these sectors it is necessary to understand fundamental properties and critical processes at a range of length scales and dynamically and link these to the materials' performance. It is in this underpinning space that the CDT-ACM fits.

The impact of the CDT will be wide reaching, encompassing all organisations who research, manufacture or use advanced materials in sectors ranging from energy and transport to healthcare and the environment. Industry will benefit from the supply of highly skilled research scientists and engineers with the training necessary to advance materials development in all of these crucial areas. UK and international research facilities (Diamond, ISIS, ILL etc.) will benefit greatly from the supply of trained researchers who have both in-depth knowledge of advanced characterisation techniques and a broad understanding of materials and their properties. UK academia will benefit from a pipeline of researchers trained in state-of the art techniques in world leading research groups, who will be in prime positions to win prestigious fellowships and lectureships. From a broader perspective, society in general will benefit from the range of planned outreach activities, such as the Mary Rose Trust, the Royal Society Summer Exhibition and visits to schools. These activities will both inform the general public and inspire the next generation of scientists.

The cohort based training offered by the CDT-ACM will provide the next generation of research scientists and engineers who will pioneer new research techniques, design new multi-instrument workflows and advance our knowledge in diverse fields. We will produce 70 highly qualified and skilled researchers who will support the development of new technologies, in for instance the field of electric vehicles, an area of direct relevance to the UK industrial impact strategy.
In summary, the CDT will address a skills gap that has arisen through the rapid development of new characterisation techniques; therefore, it will have a positive impact on industry, research facilities and academia and, consequently, wider society by consolidating and strengthening UK leadership in this field.