Graphene is not a semiconductor in its natural state. It is classified as a semimetal, specifically a zero-gap semimetal, because it lacks the energy gap between its filled and empty electron bands that defines a true semiconductor. However, researchers have developed several ways to force a bandgap open in graphene, effectively converting it into a semiconductor, and a 2024 breakthrough demonstrated a graphene-based semiconductor with performance far exceeding silicon.
Why Graphene Is a Semimetal
The distinction comes down to band structure, which describes the range of energies electrons can occupy in a material. In a semiconductor like silicon, there is a gap between the energy levels filled by electrons (the valence band) and the higher energy levels where electrons can move freely and conduct electricity (the conduction band). Electrons need a push of energy to jump across that gap, which is what allows semiconductors to switch between conducting and insulating states. That switching ability is the foundation of every transistor and computer chip.
Graphene’s band structure is fundamentally different. Its two bands meet at special points called Dirac points, forming a pair of cone shapes whose tips touch. At these points, the energy gap is exactly zero. Electrons in graphene behave almost like massless particles, moving at roughly one million meters per second near those cone tips. This gives graphene extraordinary electrical conductivity, but it also means there is no “off switch.” You cannot stop current from flowing through graphene the way you can with silicon, which is exactly what a transistor needs to do.
Why the Bandgap Matters for Electronics
A good transistor material needs a bandgap of roughly 1 electron volt (eV). That gap lets the material toggle cleanly between conducting and insulating when a voltage is applied. Silicon has a bandgap of about 1.1 eV, which makes it ideal for this purpose. Without any gap at all, graphene-based transistors cannot fully turn off, meaning they leak current constantly. That makes pure graphene unsuitable for digital logic circuits, despite its remarkable speed and conductivity.
This zero-gap problem has been graphene’s central limitation since its isolation in 2004. Researchers recognized early on that if they could pry open even a modest bandgap without destroying graphene’s speed advantage, it could outperform silicon in nearly every metric that matters for electronics.
How Researchers Force a Bandgap Open
Several strategies can turn graphene from a semimetal into something that behaves like a semiconductor. Each involves altering graphene’s structure or environment in some way.
Cutting Into Nanoribbons
Slicing graphene into extremely narrow strips, called nanoribbons, confines electrons and opens a bandgap that depends on the ribbon’s width. Narrower ribbons produce larger gaps. Measurements on ribbons of different widths grown on gold surfaces show a clear trend: a ribbon roughly six carbon atoms wide has a bandgap of about 1.69 eV, while a ribbon fifteen atoms wide drops to about 1.03 eV. This puts the wider ribbons in a range comparable to silicon and useful for transistor applications. The challenge is manufacturing these ribbons with atomic precision at scale.
Chemical Doping
Replacing some of graphene’s carbon atoms with other elements can break the symmetry that keeps the bandgap closed. One approach substitutes boron and nitrogen atoms into the carbon lattice. Researchers growing graphene films with low concentrations of boron-nitrogen dopants have achieved bandgaps as high as 600 millielectron volts (0.6 eV). That is smaller than silicon’s gap but large enough for certain electronic applications.
Growing Graphene on Silicon Carbide
The most dramatic recent result came from a team at Georgia Tech, published in Nature in early 2024. By growing graphene on specially prepared single-crystal silicon carbide, they produced what they call semiconducting epitaxial graphene. This material has a bandgap of 0.6 eV and room-temperature electron mobilities exceeding 5,000 square centimeters per volt-second. That mobility figure is ten times higher than silicon and twenty times higher than other two-dimensional semiconductors. In practical terms, electrons move through this material with far less resistance, which translates to faster switching speeds and lower heat generation in electronic devices.
How Graphene Compares to Silicon
Pure graphene’s electron mobility can reach tens of thousands of square centimeters per volt-second under ideal conditions, dwarfing silicon’s roughly 1,400 for electrons. But that comparison is somewhat misleading, because pure graphene cannot function as a semiconductor. The real comparison is between silicon and the engineered forms of graphene that do have a bandgap.
Standard epitaxial graphene grown on silicon carbide, without the special treatment used in the Georgia Tech work, shows room-temperature mobilities of about 900 square centimeters per volt-second at typical carrier densities. That is comparable to silicon but not dramatically better. The semiconducting epitaxial graphene from the 2024 study, at over 5,000, represents a genuine leap. If that material can be manufactured reliably in commercial chip fabrication, it could enable electronics that run significantly faster and cooler than today’s silicon-based chips.
Other 2D Semiconductors in the Picture
Graphene is not the only atomically thin material being explored for electronics. A family of materials called transition metal dichalcogenides already function as semiconductors without any engineering tricks. Molybdenum disulfide, for example, has a bandgap that ranges from 1.2 eV in bulk form to as high as 2.5 eV as a single layer. Tungsten diselenide sits between 1.2 and 1.65 eV depending on thickness. These values fall in the sweet spot for transistor applications.
The tradeoff is speed. These materials have much lower electron mobilities than graphene. Molybdenum disulfide transistors, while functional, are far slower than what graphene-based devices could theoretically achieve. Black phosphorus offers a middle ground, with predicted mobilities up to 26,000 square centimeters per volt-second for certain charge carriers, though experimental devices have reached only about 1,000 so far. Each material occupies a different point on the spectrum between having a usable bandgap and having fast-moving electrons, and no single material yet combines the best of both as well as researchers would like.
The Short Answer
Graphene in its pure, unmodified form is not a semiconductor. It is a zero-gap semimetal with no ability to switch current on and off. But the line between “not a semiconductor” and “semiconductor” has become increasingly blurry as engineered forms of graphene, particularly the epitaxial graphene grown on silicon carbide, demonstrate genuine semiconducting behavior with performance metrics that outpace silicon. Whether graphene will eventually replace silicon in commercial electronics depends less on physics, which increasingly looks favorable, and more on whether these engineered forms can be produced at the scale and cost that chip manufacturing demands.