Diamonds Could Be The ‘Crown Jewel’ In Future Electronics
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Diamonds could be everyone’s best friend with new research unlocking hidden properties for next-generation electronics.
Associate Professor Dongchen Qi from the QUT Centre for Materials Science led research that transformed the intrinsically inert diamond into a powerful semiconductor capable of sustaining very high-power and withstanding conditions too extreme for silicon devices.
The discovery could herald future electronics with powerful new properties that will enable next-generation military, aerospace and telecommunications applications.
“Diamond, beyond its allure as jewellery, can withstand high-voltage, high-power operations and harsh conditions such as extreme coldness in deep space or high-temperature in electricity grids, for example, but it has no intrinsic conductivity.
“Conductivity is the basis of any electronic device and, without it, diamonds are just very basic insulating materials.
“We’ve developed technology that modifies the diamond surface to make it conductive and easily controllable, which means we can now start building electronic circuits on its surface,” Qi said.
Diamond semiconductors would enable very high-power and high-frequency signal amplification and energy conversion unattainable by other semiconductor materials, making them ideal for applications such as satellite communication and broadcasting stations.
“Believe it or not, current radio and TV stations still use hundred-year-old technology called vacuum tubes — bulky glass tubes used to control and amplify signals,” Qi said.
“Silicon chips aren’t used in these applications simply because they cannot sustain high-power operations, but diamond could.”
Almost all computer chips are built on silicon, a first-generation semiconductor, according to Qi, but diamond is among third-generation semiconductors capable of sustaining higher power operations.
“People working on telecommunication or power conversion are looking at using gallium nitride or silicon carbide semiconductors, but diamonds could be a cheaper and more energy-efficient option.”
The QUT research also forms part of an Australian National Fabrication Facility (ANFF) Space Technology Prospectus supplied to NASA for discussions on fundamental research to address operating challenges for electronics in space.
“In deep space applications temperatures can range from a few hundred degrees to minus 100 degrees Celsius,” Qi said.
“Normal silicon devices would fail but diamonds are very resistant to this kind of harsh temperature change, and also to cosmic rays and solar radiation.”
Doping diamonds
Qi’s research team innovated a technique called surface transfer doping by introducing a metal oxide layer just a few atoms thick to withdraw electrons from the diamond surface to enable conductivity.
“Diamond is like a city with a fantastic highway infrastructure but no vehicles. In the materials world we call the vehicles charge carriers,” Qi said.
“Our research put vehicles on the diamond roads by introducing charge carriers through the surface acceptors.
“The metal oxide surface acceptors allow us to extract electrons from the diamond surface, leaving holes — a type of charge carrier with positive charge — to make it conductive.
“We can control the surface conductivity of diamond by increasing or decreasing the number of carriers on the road, which we can do by changing the type and coverage of the metal oxide layer.”
Researchers had to select suitable surface acceptors with an energy level matching that of diamond.
“We started with organic materials, but certain metal oxides worked best with the desired stability in practical devices,” Qi said.
Qi is also a Senior Lecturer and Australian Research Council (ARC) Future Fellow within the QUT School of Chemistry and Physics. Findings, recently published on Applied Surface Science, were part of his Enabling Diamond Nanoelectronics with Metal Oxide Induced Surface Doping project funded through the ARC Future Fellowships scheme.
Spintronics spin-off from 2D surface phenomenon
Engineering the diamond surface to accept charges also produced an unexpected quantum mechanical phenomenon that could have implications for information technologies.
Qi’s research found that holes confined to the diamond surface formed a two-dimensional (2D) layer that produced a relativistic effect called spin-orbit coupling.
Like the spinning Earth orbiting the Sun, spinning electrons can orbit atoms but generate different energy levels through this interaction.
“Spin-orbit coupling usually happens in heavy-element materials but carbon, which makes up diamond, is such a light element that the effect should have been small.
“The confinement of hole charges to the diamond surface actually induced this phenomenon and gave rise to a very strong effect.”
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Observing spin-orbit coupling required an extremely low temperature of only a few Kelvins — minus 270 degrees Celsius — which placed stringent requirements on the device architectures, according to Qi.
“We found diamond devices with palladium electrodes could operate in this extremely low-temperature environment and allow us to observe this intriguing phenomenon.”
Controlling the spin of charge carriers is at the heart of a new spintronics technology that would enable faster and more energy-efficient electronic devices.
“A stronger spin-orbit coupling in diamond means we can control the spins of holes more easily with an electric field,” Qi said.
“That would allow us to fabricate energy-efficient spintronic devices using diamond. That’s perhaps much further away from real applications but is fascinating from a fundamental physics point of view.”
The research was a collaboration between QUT, La Trobe University and the University of Melbourne. Findings were published in Carbon as ‘Strong spin-orbit interaction induced by transition metal oxides at the surface of hydrogen-terminated diamond’ and appear in the August 2020 edition.
Growing diamonds large enough to use in electronics
While diamonds have a combination of properties that make them ideal for electronic devices, Qi hopes the success in achieving a diamond device platform will accelerate complementary research in growing diamond wafers large enough for industrial applications.
“We need large diamond substrates if we are to fabricate millions or billions of devices at the same time for cost efficiency, but the most common synthesised diamond wafer is only a few millimetres across,” Qi said.
“Nowadays, people can grow very high-quality diamond with a process called chemical vapour deposition (CVD), feeding hydrocarbon gases like methane with plasmas to grow diamond.
“It is a very slow process and only produces smaller crystals, so researchers around the world have been working on growing larger diamond wafers but the technology is not quite there yet.”
Learn more
Explore more QUT research at www.qut.edu.au/research/our-research
Contact Associate Professor Dongchen Qi at staff.qut.edu.au/staff/dongchen.qi
