Graphene is a single layer of carbon atoms arranged in a hexagonal lattice, and it is considered a two-dimensional material. It is a basic structural element of other carbon allotropes like graphite, carbon nanotubes, and fullerenes.
Graphene is a promising material for electronics due to its unique properties, such as high conductivity and mechanical strength. However, integrating graphene into semiconductor devices poses significant challenges, and progress in this area has been a subject of ongoing research.
But recently Scientists have successfully created a working and scalable semiconductor using graphene for the first time.
The achievement opens the door to a potential revolution in computing, introducing a new type of computer with enhanced speed and efficiency compared to the current silicon chip technology.
The semiconductor chips are increasingly emerging as pivots of the global economy, and are described as the 'new oil' of the technology age. The computing power accessed through microchips, from data centres to smartphones, is required for all parts of the economy.
"Walter de Heer, Regents' Professor of physics at Georgia Tech, led a team of researchers based in Atlanta, Georgia, and Tianjin, China, to produce a graphene semiconductor that is compatible with conventional microelectronics processing methods — a necessity for any viable alternative to silicon," an official readout by the Georgia Institute of Technology said.
Silicon semiconductors are reaching their limit
Classical computers like the chip in your phone or laptop use electricity flowing through silicon switches to represent ones and zeros—also known as bits.
“Semiconductors are essential to allow all computers to function. They allow us to create tiny switches which can be turned on and off to allow the flow of electricity. It is this electricity flowing through electrical circuits that allows computers to perform calculations,” said Sarah Haigh, professor of materials at the National Graphene Institute, University of Manchester, UK.
We use silicon semiconductors every time we use a credit card, start a car, open doors on buses and trains and of course use a smartphone or laptop. But silicon semiconductors have their limitations, which has led scientists to search for a new material.
“Silicon electronics require a fairly large amount of power and energy, including energy needed to cool the electronics when energy is emitted as heat,” said Haigh.
Graphene: Wonder material
One option was graphene. Graphene is a single sheet of carbon atoms—a 2D material held together by the strongest chemical bonds known. These carbons are arranged in tessellated hexagons, much like honeycomb.
It is an incredibly strong material—about 200 times stronger than steel. It’s so strong you can hold up a football with just one atomic layer of graphene. Graphene is also incredibly flexible, making it ideal for use in electrical devices and batteries, or even printed on glass, plastics or fabrics. But its potential to be used as a faster and more energy-efficient semiconductor has excited scientists the most.
“The possibility to retain graphene’s exceptional speed as well as the efficiency of the conduction of electrons without requiring large amounts of energy offers huge potential for it to be used to create ‘beyond silicon’ electronics where computers are faster and use less energy to run,” said Haigh.
First functional graphene semiconductor
Graphene has major drawbacks, which has prevented its use in electronics. One major issue is known as the “band gap problem.” Haigh said. “Scientists in the field have been trying to realize the exceptional conductivity of graphene in electronic circuits for over a decade”.
The band gap is a crucial electronic property that allows semiconductors to switch on and off. Graphene didn’t have a band gap—until now. De Heer’s team figured out how to grow graphene on special silicon carbide chips. The research took 10 years, as the team refined materials and altered graphene’s chemical properties until they achieved the perfect structure.
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| Graphene characteristics |
Finally, the graphene was able to act like a high-quality semiconductor that rivalled silicon. “The good thing about graphene is, not only can you make things smaller and faster and with less heat dissipation, you’re using properties of electrons that are not accessible in silicon. So this is a paradigm shift—it’s a different way of doing electronics,” said de Heer.
Challenges in development of Graphene semiconductors
Graphene, composed of a single layer of carbon atoms, boasts remarkable strength surpassing that of steel at comparable thicknesses. It is an exceptional electrical conductor and exhibits high resistance to heat and acids.
Despite these advantages, scientists have struggled to develop a working graphene semiconductor that can be controlled to conduct or insulate electricity at will, a crucial element for creating the logic chips powering computers.
The primary obstacle has been the absence of a bandgap—a critical feature in semiconductors allowing for the controlled flow of electrons.
Graphene had shown promise as a semiconductor on a small scale in previous research, but upscaling to practical computer chip sizes proved challenging.
However, recent work led by Walter de Heer and his team at Georgia Tech in Atlanta has marked a significant breakthrough.
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| Graphene gas sensor fabrication |
How Graphene semiconductors were made?
Using silicon carbide wafers heated to evaporate the silicon before the carbon, the researchers led by Walter de Heer and his team at Georgia Tech in Atlanta successfully created graphene with a bandgap.
They even demonstrated a functional transistor—a fundamental component acting as an on/off switch for the flow of current.
A general overview of some common methods used in the production of graphene and graphene-based semiconductors :
- Chemical Vapor Deposition (CVD): This method involves growing graphene on a substrate by exposing it to a carbon-containing gas, such as methane, in the presence of a metal catalyst. The carbon atoms then precipitate onto the substrate, forming a graphene layer.
- Liquid Phase Exfoliation: This technique involves dispersing graphite in a liquid medium and then using sonication or other mechanical means to break down the layers into graphene sheets. The resulting graphene dispersion can be deposited onto a substrate.
- Mechanical Exfoliation (Scotch Tape Method): This is a simple method where a piece of adhesive tape is used to peel off thin layers of graphene from a graphite crystal. While effective for producing high-quality graphene, it is not suitable for large-scale production.
- Chemical Exfoliation (Hummers' Method): This method involves oxidizing graphite with strong acids and then reducing the resulting graphene oxide to obtain graphene. However, this process often produces graphene with functional groups, which may need additional treatment for certain applications.
- Epitaxial Growth: In this method, graphene is grown on a silicon carbide (SiC) substrate through a high-temperature process. The silicon atoms in the SiC substrate sublimate, leaving behind a layer of graphene.
Once graphene is produced, additional steps may be taken to modify its properties and create graphene-based semiconductors. The integration of graphene into semiconductor devices often involves precise fabrication techniques, such as lithography and doping processes, to create functional electronic components.
Faster, more energy-efficient electronics
Experts say the innovation holds huge potential for the electronics industry. For one thing, it could allow us to create new graphene semiconductors which are much more powerful, but use less energy than their silicon counterparts.
“Graphene electronics are more efficient because they can require less energy to switch on and off. They also allow electrons to flow without creating a lot of unwanted heat that has to be cooled with fans [requiring energy],” said Haigh. “This would mean phones could last for weeks without running out of battery, reduce energy consumption in all parts of our lives, reducing costs and the pollution from fossil fuels,” she added.
De Heer said his discovery could change the future of electronics. For one, the new graphene superconductors could accelerate the development of quantum computing technologies. Quantum computers can solve problems in seconds that would take ordinary supercomputers millennia to do, but they’re still in development. Experts say graphene semiconductors could help overcome the many challenges of creating quantum computers.
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