Graphene + Hexagonal Boron Nitride = New Transistor

Graphene has been fascinating to scientists since its discovery more than a decade ago. This carbon material with only one atomic thickness has excellent electronic properties, strength and ultra-lightweight. Its use is also expanding, but how to implant the energy gap (bandgap/semiconductor or insulator valence band tip to the energy gap at the bottom of the conduction band) to make transistors and other electronic devices, but always let the researchers do nothing.

Graphene 

Researchers at the Massachusetts Institute of Technology (MIT) have made major breakthroughs in this area and are even expected to change some of the theoretical predictions of graphene physics. They introduced another material with single atomic thickness and properties similar to graphene: hexagonal boron nitride (HBN). They placed a layer of graphene on the HBN, and the resulting hybrid material had both the conductive properties of graphene and finally the energy gap necessary to build the transistor.

hexagonal boron nitride

Pablo Jarillo-Herrero, assistant professor at the MIT Department of Physics, said: "By combining these two materials, we have obtained a hybrid material. Graphene is an excellent conductor, and hexagonal boron nitride is a good insulator that blocks electron circulation. Putting them together, we get high-quality semiconductors."

But the whole process is obviously not as simple as 1+1=2. Researchers must almost perfectly align the atomic frames of the two materials. They both have a hexagonal structure and the size (lattice constant) is almost the same, so the two atomic frames can be perfectly spliced together from the fine point, but the size of hexagonal boron nitride is 1.8% larger than graphene, so from a large scale, there will still be some differences. There is currently no perfect solution for this, and the researchers say that they can only rely on obtaining angular alignment, but there is always a chance of about 1/15 error.

Ray Ashoori, a professor at the MIT Department of Physics, said: "The most amazing thing we found is that a slight adjustment of the angle between the layer of material and the other layers can obtain materials with a variety of different electronic properties."

Prior to this, some people cut the graphene layer into thin strips to make it into a semiconductor, but this would greatly weaken its electrical properties. The above-mentioned methods do not have such drawbacks, but the current energy gap is still not practical, and further improvement is expected to become a method for manufacturing new materials for transistors.

In addition, the MIT team found an interesting physical phenomenon in the newly obtained material: When exposed to a magnetic field, it presents a fractal trait, the so-called "Hofstadt Butterfly Spectrum", which was once thought to be impossible in theory.

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