Imagine having a road without traffic lights where cars can move freely without stopping. In a similar fashion, electrons in graphene can move unimpeded because of what’s known as a “zero bandgap.” However, this feature is not always desirable.
Graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Despite its extraordinary electrical, thermal, and mechanical properties, the need to control the flow of electrons—much like using traffic signals to manage the flow of cars—has prevented graphene from being utilized in the semiconductor manufacturing used in devices like transistors. Until now, silicon has dominated this market due to its “bandgap,” despite its other shortcomings.
For years, scientists have sought to induce a bandgap in graphene by adding “traffic signals” that would allow controlled stop-and-go mechanisms in electronics. A research team from the Georgia Institute of Technology in the United States claims to have succeeded, producing the world’s first functional semiconductor made from graphene, overcoming a major obstacle that had plagued graphene research for decades and led many to believe that graphene electronics would never become a reality.
Graphene is an amazing flat material with strong bonds that can be manipulated on the smallest scale (Georgia Institute of Technology)
How Did Scientists Introduce a “Traffic Signal” into Graphene?
In a study published in the journal Nature, the researchers announced the details of their decade-long research project culminating in the successful introduction of a “bandgap” into graphene, effectively installing a “traffic signal” to control electrical flow.
This achievement involved the use of a technique called “epitaxial growth” to cultivate graphene on silicon carbide wafers using special ovens, producing epitaxial graphene endowed with the sought-after bandgap property.
“Epitaxial growth” is a materials science and semiconductor manufacturing process that deposits a thin crystalline layer on a substrate in a manner that maintains structural alignment between the deposited material’s atoms and the substrate’s atoms.
The process can be summarized in the following steps:
- The Substrate: Typically made of silicon or another crystalline material.
- The Source Material: Introduction of a source material to prepare a thin layer on the substrate.
- The Deposition Process: Techniques like chemical vapor deposition or molecular beam epitaxy are used to deposit the source material on the substrate.
- Alignment with the Substrate: The deposited atoms or molecules arrange themselves to mirror the crystal structure of the substrate, an alignment essential to maintaining the substrate’s characteristics in the thin layer.
- Single Crystalline Layer: As deposition continues, a single crystalline layer of the material forms atop the substrate.
The researchers were able to use this technique to deposit a graphene layer in a way that preserves the crystalline structure of the silicon carbide substrate, resulting in epitaxial graphene with semiconductor properties, making it compatible with traditional electronic processing methods and suitable for electronic applications.
Epitaxial graphene based on silicon carbide, with electronic semiconductor properties (Nature Journal)
Faster and More Efficient Computing
After this breakthrough, the researchers used a technique known as “doping” to continue studying the electronic behavior of the new graphene material.
This technique involves introducing specific atoms into the graphene, which “donate” electrons. By adding these electron-donating atoms, the researchers could measure the electronic properties of the graphene without causing damage to its structure.
According to the study, graphene semiconductors exhibited mobility ten times greater than silicon, allowing electrons to move faster with lower resistance, making computing faster and more efficient.
This achievement could lead to a significant shift in electronics, possibly replacing silicon in future electronic devices.
Professor Walt de Heer, from the School of Physics at Georgia Institute of Technology and the leading researcher in the study, compares the potential impact of graphene electronics to historic shifts in electronic technologies, such as the transition from vacuum tubes to silicon.
De Heer said in a press release by Georgia Institute of Technology that this achievement represents a significant technological milestone akin to the Wright brothers’ first successful flight, with people questioning the need for flight when fast trains and boats already existed. Yet, they persisted, and that was the beginning of a technology allowing people to travel across oceans.
De Heer believes graphene could represent the next generation of electronics, due to its unique properties that would enable faster and more efficient computing.
(Video: Professor Walt de Heer from the School of Physics at Georgia Institute of Technology tells the story of the achievement.)
A Starting Point Towards Rapid Ascent
This achievement raises several key questions related to:
- How silicon carbide helped graphene overcome the challenge of lacking a “bandgap,” a crucial property for turning semiconductor-based devices on and off?
- How does the method used by the researchers to grow graphene on silicon carbide wafers differ from previous attempts to create graphene-based semiconductors?
- What limitations does silicon face in the context of modern electronics, prompting the search for alternative materials like graphene?
- How do graphene semiconductors differ from silicon, particularly concerning their ability to conduct, transfer, and dissipate heat?
- What challenges might graphene face when scaling the concept towards practical use in nanoelectronic electronics?
Al Jazeera Net presented these questions to Professor De Heer via email. In his response to the first question, he noted that graphene’s chemical bond with silicon carbide changes the electronic structure of graphene, endowing it with the required “bandgap” for electronics.
Regarding the second question, he mentioned past attempts to chemically alter graphene through reactions with hydrogen, for instance, that resulted in a rather poor semiconductor, not suitable for electronics. Their achievement stands out as they achieved properties surpassing the most commonly used material, silicon.
In answering the third question, he listed three reasons why the world seeks alternatives to silicon:
- Silicon doesn’t help devices become smaller.
- The heat generated in silicon devices becomes excessive.
- The processor speeds in silicon devices cannot get any higher.
On the fourth question about the advantages of graphene-based semiconductors over silicon, he pointed out that graphene is an incredible flat material with strong bonds that can be manipulated on the smallest scale. It can function as semiconductors or metals and its unique properties can be used to create fast, thin electronic devices, potentially surpassing those currently in use with silicon.
Finally, in response to the fifth question, he admitted that what they have done is merely a starting point toward a world of much smaller and faster-performing electronics, emphasizing that at least a decade of further research is needed to produce high-quality, commercial nanoelectronic devices based on graphene.
