The rapidly expanding market for better power semiconductors at present is supplied by silicon and gallium nitride semiconductors. Power semiconductors switch electrical current in a device at high voltages, thereby converting and controlling the electricity. The use of silicon carbide (SiC) semiconductors is gaining interest because they work at much higher power loadings and temperatures, reducing energy loss and increasing the life of devices. Silicon carbide power semiconductors are applied in various industries including automotive, consumer electronics, IT and telecommunication, military and aerospace, and power. They are increasing in popularity in green energy applications such as electric cars and wind turbines.

SiC semiconductors are grown in reactors by a process called MOCVD (Metal Organic Chemical Vapour Deposition). As part of this process SiC wafers are mounted onto a coated graphite substrate. A common used method to coat the graphite substrate is chemical vapour deposition (CVD). The coating forms a protective barrier to prevent impurities from the graphite affecting the growth process. Recent developments have demonstrated great promise with tantalum carbide (TaC) as a graphite coating due to its properties as a non-porous material with a very high melting point. These properties produce an extremely reliable and durable protective coating at low cost compared with other compound coatings currently in use. The outcome is a more reliable and efficient growth process with increased output of SiC semiconductors.

Aixtron, the world-leading manufacturer of MOCVD reactors for SiC semiconductors, has approached Advanced Furnace Technology (Aftech) to optimise the processes of coating graphite parts with TaC for their MOCVD reactors in the production of SiC semiconductors. The potential for a successful project of this kind would increase the position of Aftech and the UK in the growth markets for SiC semiconductor applications such as solar and wind power, and electric vehicles. Currently Asia-Pacific is dominating the global market and the US Department of Energy is investing millions into various innovative projects (source: Mordor Intelligence).

Aftech were approached by Aixtron to carry out this project for two main reasons. Firstly, the failures of current Aixtron suppliers, i.e. in South Korea and the USA. These include delamination (unsticking) of the TaC coating from the graphite substrate, as well as the failure to manufacture parts to scale due to restricted sized furnaces and a lack of capacity to build new, appropriate instruments. Secondly, Aftech possess the relevant experience and expertise to overcome these challenges.

The major advantages that Aftech holds over its competitors include the capacity to build its own high temperature furnaces and systems and its experience in developing CVD systems, depositing chemicals such as tungsten carbide, aluminium gallium nitride, gallium arsenide, gallium phosphide, as well as silicon carbide. Aftech is unique in these respects and this provides us with a considerable advantage to optimise the processes of TaC coated graphite as well as manufacturing the end product.

We see this as a major opportunity to bring in a new and effective product with a team headed by Dr Zoe Tolkien, who has been successfully working as our research and development officer on projects for optimising coating processes with pyrolytic graphite as well as graphite purity. She has shown great tenacity and promise in this role so far and we are confident in promoting her to develop her talents further through this project.

Potential Impact:
The beneficiaries of the innovation include Aftech, the specialist academic facilities, i.e. the Universities of Cambridge and Bristol, the silicon carbide (SiC) semiconductor industry, and the renewable energy industry.

For Aftech, the innovation will create a new division to support the continuation of a company that relies on continual innovation for survival in its industry. The novelty of the product will secure Aftech's position as a major player in the supply chain of the rapidly expanding manufacture of SiC semiconductors. By leading the project, Dr Tolkien will be able to support the continuation of Aftech. Her acquired expertise and leadership throughout the project will position her to take over from current staff, of 40 years' employment, who are due to retire taking with them a huge amount of experience and expertise. The innovation will plug this gap by supporting a new generation of experience and expertise, upon which the company relies so greatly.

The University of Bristol and the University of Cambridge, specialist facilities in the project, will benefit from the research by furthering knowledge of the microstructure and mechanics of graphite and graphite-coated materials. They will be able to apply this knowledge to areas of research outside of the SiC semiconductor market, thereby broadening the applications of the innovation. The newly acquired knowledge will also generate research outputs such as academic papers for conferences and publication, and will support career progression amongst researchers.

The innovation will benefit the broader SiC semiconductor market because of the integral role played by TaC coated graphite parts (i.e. 'satellites' and 'susceptors'). In broad terms, these parts support the growth of the SiC semiconductors in a MOCVD reactor. The parts are used various times before they are either cleaned by a chemical process or replaced. Eventually all parts have to be replaced and so their lifecycle is critically important. The role of these parts is to enable consistent reproduction of the SiC semiconductors. The coating is important as it prevents the impurities of the graphite from adversely affecting the growth process and prevents aggressive gases from attacking the graphite. Therefore, as well as lifecycle, performance is also critical. The innovation will increase both the lifecycle and performance of the satellites and susceptors, thereby supporting growth of the SiC semiconductor industry through increased efficiency and lowered costs.

The innovation will benefit the renewable energy industry by expediting the replacement of other energy industries with a high environmental impact. SiC semiconductors are highly suitable for power electronics as required by electric cars, solar energy convertors and other applications. The increased manufacture and lowered costs of SiC semiconductors enabled by the innovation will increase the possibility of more affordable applications. Manufacturers of these applications, i.e. electric cars and solar energy converters, will be able to increase production, thereby lowering costs and increasing adoption by the general public. Society will also benefit by greater adoption by the public of these applications, through greater quality of life, health and wellbeing.

The key results of the innovation project, such as specific heating temperatures, will not be directly disseminated to the beneficiaries as the commercial sensitivity of the work is crucial to its success. However, it is important that the research data generated by the universities of Cambridge and Bristol are available to them to publish and disseminate in the furthering of academic discovery and excellence. The timescales of impact for Aftech, and the universities of Cambridge and Bristol are within the period of the innovation project. The timescales of impact for both the SiC semiconductor and the renewable energy industries are within a year of the end of the project.