Graphene Semiconductors – Are They Finally Here?

Today, semiconductors power the modern world. They are the backbone of electronic devices, and a discovery aims to transform the electronic industry substantially. 

Also referred to as microchips or integrated circuits (ICs), semiconductors are materials that have an electrical conductivity that falls between that of conductors like aluminum and copper and insulators like ceramics and glass.

Semiconductors are sensitive to light and heat, and their resistance varies. The resistivity of a semiconductor falls as its temperature rises, in contrast to how metals behave.

Some examples of semiconductors include silicon and germanium, which are pure elements and can easily be found in nature. Then, there are compounds like cadmium selenide and gallium arsenide. Also, to alter the conductivity or properties of materials, small amounts of impurities are added to pure semiconductors via a process called doping.

So, depending on their purity, semiconductors are classified into — intrinsic semiconductors, which are natural materials made of one single type of atom and can be used directly in devices, and extrinsic semiconductors, which need to be doped first in order to be used in devices. Transforming intrinsic semiconductors brings two types of extrinsic semiconductors: N-type or donors and P-type or acceptors.

Semiconductors are used for diodes, which convert alternating current into direct transistors or current amplifiers, and electronic circuits, which are essential in the manufacture of different types of electronic devices.

With semiconductors, we get the advantage of having no filaments. As such, they do not need to be heated to emit electrons. This also means that semiconductors can be operated immediately. Moreover, they are small in size; hence, they are compact, portable, and utilize less power. Also, semiconductors are not very expensive.

Semiconductors are an integral part of our lives, as without them, there would be no TV, radio, computers, smartphones, automobiles, refrigerators, and video games. Semiconductors basically allow the creation of tiny switches that can be turned on and off to control the flow of electricity as this electricity flowing through electrical circuits allows electronic devices to function.

This makes semiconductors an essential component of electronic devices to enable advances in computing, communications, healthcare, transportation, clean energy, defense, appliances, gaming hardware, and many other applications.

Over the past many decades, developments in semiconductor technology have made these electronic devices not just smaller but also faster and more sophisticated, compatible, and reliable.

Companies working with semiconductors generally organize their activities either around design or manufacturing. Those that focus on design are referred to as “fabless” firms, while those focusing only on manufacturing are called “foundries,” and those that do both are called Integrated Device Manufacturers, or IDMs.

Over the past few years, there has been a semiconductor crisis. Ever since late 2020, after the pandemic and lockdowns, as the demand for electronic devices surged, there has been a shortage of microchips and electronic circuits globally. 

While online classes, remote work, and increasing digitization caused enormous growth in the demand for electronic devices, new technological advances have led to disruptive technologies like AI, VR, 5G, big data, and cloud services that have further exacerbated the situation. 

In response to this, companies around the world are investing huge amounts of resources to find a solution to the problem. 

A Big Discovery: The First Functional Graphene Semiconductor 

Gallium arsenide is a popular semiconductor used in solar cells, laser diodes, and microwave-frequency integrated circuits. The most common semiconductor in use today, however, is Silicon, which plays a critical role in fabricating most electronic circuits. But the material is reaching its limit — it requires a large amount of power, which has scientists working on finding an alternative.

And there is another element, graphene, which isn't considered a semiconductor but can be used to make chips and circuits. It is a highly conductive material that very effectively dissipates heat, improving the performance of electronic components. It also has superior speed and energy efficiency compared to silicon without needing large amounts of energy, making it extremely beneficial to use in creating electronics.

Graphene is an extremely thin material, just one atom thick layer of carbon arranged in hexagons, and is the foundation for graphite. Despite being the thinnest material known to man, it is very tough (about 200 times stronger than steel) and flexible. 

Not to mention, this single sheet of carbon atoms is a great conductor of heat and electricity and possesses some interesting light absorption abilities. Hence, this material has the potential to revolutionize many applications, including sensors, solar cells, batteries, and more.

However, the material is not without its issues, which include graphene's exceptional electrical conductivity, which makes it difficult to use as a semiconductor. So, it needs a bandgap, which allows semiconductors to switch on and off, that it doesn't usually have. To introduce bandgap to graphene, scientists have fabricated graphene in specific shapes or used other 2D materials that have an inherent bandgap with the material but have failed to produce viable semiconducting graphene. 

As scientists work with graphene, a breakthrough was made recently where researchers demonstrated the first functional graphene semiconductor, which means changing the world of computing and electronics forever. This was achieved by overcoming the hurdle that was affecting graphene research for many years, having the right band gap that could switch on and off at the correct ratio — presenting a pivotal stage in making graphene chip-based electronics a reality.

The graphene semiconductor with a band gap is not only functional but can also be integrated into existing manufacturing processes. Published in Nature in the first week of 2024, the study showed a functional graphene semiconductor that can be used in nanoelectronics.

For this, Walter de Heer, a physics professor at the Georgia Institute of Technology, led a research group and collaborated with China's Tianjin University. And he said:

“We now have an extremely robust graphene semiconductor with ten times the mobility of silicon, and which also has unique properties not available in silicon. But the story of our work for the past ten years has been, ‘Can we get this material to be good enough to work?'”

Early in his career, De Heer began by exploring carbon-based materials as potential semiconductors, then shifted to 2D graphene over twenty years ago. The team was “motivated by the hope of introducing three special properties of graphene into electronics” — an extremely robust material, its ability to handle very large currents, and to do that without heating up and falling apart.

The breakthrough was achieved when the team figured out how to grow graphene on silicon carbide wafers — which are utilized in electronic devices & enable efficient conversion of energy — by utilizing specialized furnaces as well as a special heating and cooling process. 

This led to epitaxial graphene, which is a layer that grows on the crystal face of silicon carbide (a hard crystalline compound containing silicon and carbon), which, when made properly, chemically bonds to the silicon carbide and shows semiconducting properties.

In order to make a functional transistor, the team has to make sure its properties are not damaged when the semiconducting material is manipulated to work as a functional transistor. For this, the team had to first see if the material was a good conductor and use the doping technique to do that, and it worked without damaging the material or its properties. 

The transition to the silicon carbide wafers, as per de Heer, is “quite feasible.” The study found that their graphene semiconductor has far greater mobility than silicon, meaning the electrons move with very low resistance. In electronics, this translates to faster computing. 

“It's like driving on a gravel road versus driving on a freeway,” de Heer said. “It's more efficient, it doesn't heat up as much, and it allows for higher speeds so that the electrons can move faster.”

Revolutionary Breakthrough to Fuel Future Electronics

It was after ten years of research that the latest study figured out how to grow graphene on special silicon carbide chips. The team altered the chemical properties of graphene to achieve the desirable structure so that the graphene can act like a high-quality semiconductor.

Talking about making graphene electronics happen, de Heer noted:

“We had to learn how to treat the material, how to make it better and better, and finally, how to measure the properties. That took a very, very long time.”

The semiconductor is currently only two-dimensional (2D) with all the necessary properties to be used in nanoelectronics. Its electrical properties are also far superior to other two-dimensional semiconductors that are currently in work. Experts believe the discovery can completely change the face of the electronics industry by allowing us to create new, powerful graphene semiconductors that use less energy than silicon.

“This research has not only maintained graphene's remarkable stability but also introduced fresh electronic traits, clearing the path for graphene-based chips,” stated Beijing-based Science and Technology Daily.

Electronics based on graphene are simply more efficient as they need less power to switch on and switch off, and on top of that, electrons can flow without producing heat that then needs to be cooled with even more energy. This means “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,” said Sarah Haigh, professor of materials at the UK's National Graphene Institute, University of Manchester, in an interview.

This could pave the way for chips that power more advanced personal computers and quantum computers in the future. 

The researchers noted in the study that electrons in this silicone alternative, much like light, have properties resembling quantum mechanical waves. These properties can very well be utilized at very low temperatures. Researchers now intend to explore this in subsequent research.

Epitaxial graphene allows electrons to move with less resistance, which means transistors made in this way can operate at terahertz frequencies. It helps overcome the limits of silicon, which includes just how fast transistors can switch on and off, the smallest they can be made, and the heat created. 

This way, the new material could cause a paradigm shift in the field of electronics, which allows for electron's quantum mechanical wave properties to be utilized, a requirement for quantum computing. A major step towards the next generation of computing, this can open the doors to a new way of building electronics that are smaller and faster.

As de Heer pointed out, it's not only graphene's ability to “make things smaller and faster and with less heat dissipation” but utilizing the “properties of electrons that are not accessible in silicon,” presenting “a paradigm shift—it's a different way of doing electronics.” 

This means another generation of electronics is now imminent. For a long time now, silicon has been leading the electronics, which was a step above vacuum tubes, which came after wires and telegraphs, and now graphene would be leading the way next.

“To me, this is like a Wright brothers moment,” de Heer said. “They built a plane that could fly 300 feet through the air. But the skeptics asked why the world would need flight when it already had fast trains and boats. But they persisted, and it was the beginning of a technology that can take people across oceans.”

Moreover, it can be scaled. Previously, graphene had shown promise as a semiconductor, but only on a small scale. Upscaling graphene semiconductors to practical computer chip sizes has been challenging. However, the latest breakthrough used a process that is similar to techniques used in creating silicon chips and is compatible with conventional microelectronics processing methods, making it more feasible to scale up.

The research used wafers, which, according to David Carey at the UK's University of Surrey, is “really, truly scalable,” and the technology used by the semiconductor industry currently can be used to “scale up this process.”

Having said that, it remains to be seen if the latest graphene semiconductors can actually perform better than the current superconducting technology. Moreover, for the world to shift to graphene chips, new research will have to be refined in regard to quality, size, and manufacturing techniques. This means it is going to be a long journey, and it can take more than a decade to fully realize the industrial implementation of graphene semiconductors.

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