Developing a deeper understanding of doping and defects in metal oxide semiconductors

Metal oxides (MO) semiconductors play a vital role in number of technology platforms ranging from large area electronics/displays through to applications as diverse as biosensing and photocatalysis. Collectively MOs provide a suite of materials with tuneable electronic properties, including charge carrier mobility and density, high optical transparency and offer access to a plethora of stable nanostructures. Furthermore, the electrical and optical properties of MOs can be further tuned by substitutional doping.
Here we propose to investigate several n-type MOs, including In2O3 SnO2, ZnO and WO3 as well as their doped analogues Fabricated by established chemical and physical deposition processes, including atomic layer deposition (ALD), chemical vapour deposition (CVD) and by emerging solution based processes all at temperatures < 450 C. Whilst the different synthetic approaches should result in compositionally similar films, we anticipate significant variation in defect chemistry and correspondingly differences in electrical and optical properties. Using the characterisation tools available in this collaborative research project we aim to address a number of interrelated research questions, namely:
- How can stable and controllable free electron concentrations be achieved through substitutional doping?
- Can we enhance and/or supress the dual role of defects i.e. reduce defect induced charge carrier recombination but enhance n-type conductivity?
- Can we improve our understanding of the interplay between intrinsic and extrinsic dopants on change carrier mobility?
- How the major defect types, their concentration and energies vary with processing conditions?

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.