Quantitative non-destructive nanoscale characterisation of advanced materials

To satisfy the performance requirements for near term developments in electronic and optoelectronic devices will require pioneering materials growth, device fabrication and advances in characterisation techniques. The imminent arrival of devices a few atoms thick that are based on lighter materials such as graphene or boron nitride and also advanced silicon and diamond nano-structures. These devices pose new challenges to the currently available techniques for producing and understanding the resulting devices and how they fail. Optimising the performance of such devices will require a detailed understanding of extended structural defects and their influence on the properties of technologically relevant materials. These defects include threading dislocations and grain boundaries, and are often electrically active and so are strongly detrimental to the efficiency and lifetimes of nano-scale devices (a single badly-behaved defect can cause catastrophic device failure). These defects are especially problematic for devices such as silicon solar cells, advanced ultraviolet light emitting diodes, and advanced silicon carbide and gallium nitride based high power devices (used for efficient switching of large electrical currents or for high power microwave telecoms). For graphene and similar modern 2D materials, grain boundaries have significant impact on their properties as they easily span the whole size of devices.

Resolving all of these problems requires new characterisation techniques for imaging of extended defects which are simultaneously rapid to use, are non-destructive and are structurally definitive on the nanoscale. Electron channelling contrast imaging (ECCI) is an effective structural characterisation tool which allows rapid non-destructive visualisation of extended crystal defects in the scanning electron microscope. However ECCI is usually applied as a qualitative method of investigating nano-scale materials, has limitations on the smallest size features that it can resolve, and suffers from difficulties in interpreting the resulting images. This limits this technique's ability to work out the nature of defects in these advanced materials.

We will make use of new developments in energy resolving electron detectors, new advances in the modelling of electron beams with solids and the knowledge and experience of our research team and partners, to obtain a 6 fold improvement in the spatial resolution of the ECCI technique. This new energy-filtered way of making ECCI measurements will radically improve the quality of the information that can be obtained with this technique. We will couple our new capabilities to accurately measure and interpret images of defects to other advanced characterisation techniques. This will enable ECCI to be adopted as the technique of choice for non-destructive quantitative structural characterisation of defects in a wide range of important materials and provide a new technique to analyse the role of extended defects in electronic device failure.

Our research programme will impact on researchers in both academia and industry who require information on the crystalline quality of their materials and subsequent electronic and optoelectronic devices, and on researchers developing new detectors and software tools for electron microscopy. Our research will result in new quantitative methods for materials characterisation, enabling for example optimisation of 2-D materials and improved performance of nitride-based electronic devices. Our project partners span researchers working on a diverse range of materials including nitride semiconductors, silicon, silicon carbide, diamond, graphene and ultrathin boron nitride thin films. While some of our co-investigators and project partners are working at the leading edge of electronic and optoelectronic device development, others are engaged in the development of next generation radiation detectors. Three of our project partners are international companies who are well placed to exploit advances we produce in electron microscopy techniques (Bruker Nano) and in materials characterisation (NXP Semiconductors UK Limited and IQE Plc). Throughout the grant period we will actively seek out new collaborators who would benefit from our new detectors and materials analysis expertise.

Where appropriate we will pursue the commercial development of our research through our industrial project partners in materials, instrumentation and software development. For example, in collaboration with Glasgow University and an industrial collaborator, we are presently preparing patents and are negotiating the licensing of our recent
novel applications of digital imaging direct electron detectors. From the simulation and analysis components of the proposal we will produce open source materials. Professional software will be packaged with associated tests and documentation and made available on a public open source repository such as GitHub or bitbucket. Bristol works closely with major semiconductor manufacturers, in particular NXP Stockport, MACOM Belfast, Element Six Didcot, ONSemi Belgium, Infineon Austria, Qorvo USA. The approaches and results
developed in this project will be discussed with these partners to feed back into their production processes. NXP is directly involved in this project and will be updated in project meetings; the other partners Bristol works with will be updated in meetings of other programmes such as the European ECSEL, EcoGaN and PowerBase events or US DARPA in one-to-one meetings to enable commercialisation.

We will engage with the wider public through participation in events held in the Glasgow and Bristol Science Centres and will continue, evolve and expand our involvement with public engagement, including work promoting science in local schools and contributions to the Glasgow and Bristol Science Festivals and European Researchers' Night. The team have a track record of giving lectures, writing articles, running workshops and quizzes, building exhibits, street busking, leading science street tours and providing kits to
schools. Specifically, to promote the research being undertaken in this project, we will provide resources on our website for teachers, school pupils and the public ranging from basic information on the physics and applications of semiconductors, through to instructions on how to make your own models of crystals and crystal defects via 3-D printing. We will also develop a Careers workshop, in collaboration with the Glasgow Science Centre, on the applications of microscopy.