Researchers find diamond could hold more charge

Paul Boughton

Researchers at the University of Glasgow have found an improved method to introduce mobile electronic charge into synthetic diamond.

The improved method will increase the stability and performance of electronic components such as transistors made from diamond and lead to a new generation of tough and durable electronic systems that could be used in space. Diamond is very resistant to radiation and either extreme heat or cold and is therefore an excellent material choice for operation in satellites and other space based technology.

Since the mid twentieth century, people have been trying to use diamond to make electrical devices because of its unique properties.  Many are aware of its extreme physical hardness but fewer are aware of its electrical properties.

For example, it possesses the highest thermal conductivity of any known solid which allows heat to flow through it more easily than any other material.  It is also extremely robust electrically, which means it can tolerate high voltages, making it better placed than other materials such as silicon for use in high power components.

As pure diamond is essentially an insulator, to make an electronic device from it, it must be 'doped' to introduce mobile charge into it so it can carry an electrical current.

Unfortunately, many of the material properties that make diamond so attractive as an electronic material also make it very difficult to dope. Although a lot of research over the past 40 years has focussed on this problem, even the best processes currently in use for this today are unstable and/or quite inefficient. This is the main reason why diamond electronics has not yet reached a level of maturity for commercialisation.

Using a process known as surface transfer doping, and by using new materials combined with diamond, the researchers have now demonstrated a much more stable and more efficient technique to overcome this problem.  The work was undertaken in the James Watt Nanofabrication Centre.

Dr Dave Moran, Lord Kelvin Adam Smith Fellow in Sensor Systems at the University of Glasgow said “The implications of this process are considerable. With these new results, the team believe they have cracked one of the main problems that has until now stopped diamond electronics from becoming a reality.

“Traditionally for surface transfer doping of diamond to work, molecules which are naturally present in the air are required to attach themselves to the diamond surface. Electrons are transferred from the diamond to this layer of molecules which in turn creates electronic vacancies in the diamond known as ‘holes’. Much like electrons, these holes can then be used to pass current through the diamond. Unfortunately electronic devices made from this process rely on exposure to air to operate and are extremely sensitive to atmospheric conditions such as temperature and humidity, which makes them very unstable.

“We have identified a set of materials that due to their extreme energy alignments provide a more efficient and robust surface material to promote surface transfer doping in diamond. As well as drastically improving the stability, we have proven that we can more than double the amount of charge flowing through diamond using this process and predict that we can increase this even more. This should lead to a substantial increase in the performance and stability of future diamond electronic components."

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