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Research Semiconductors made from graphene and boron nitride can be charge-doped using light. When the GBN heterostructure is exposed to light (green arrows), positive charges move from the graphene layer (purple) to boron nitride layer (blue).
Image Credit: DOE/Lawrence Berkeley National Laboratory

Published on May 22nd, 2014 | by James Ayre

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Graphene Boron Nitride Heterostructures Can Be Altered Using Nothing But Light, Research Finds

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May 22nd, 2014 by
 
In an important advance in the drive towards the unlocking of graphene’s noted potential, researchers have developed a technique that allows for the electronic properties of graphene boron nitride (GBN) heterostructures to be modified using nothing but light.

GBN heterostructures have been noted for their potential use in electronics (and other things) owing to their addressing of one of the main limitations of pure graphene, the lack of a band-gap — which means that the material’s conductance can’t be turned “off.” The GBN heterostructures — composed of ultrathin layers of graphene and boron nitride — are almost as fast as pure graphene, but possess a band-gap. The issue, though, is that, until now, they have been hard to produce — typically either through chemical doping or electrostatic-gating.

Semiconductors made from graphene and boron nitride can be charge-doped using light. When the GBN heterostructure is exposed to light (green arrows), positive charges move from the graphene layer (purple) to boron nitride layer (blue). Image Credit: DOE/Lawrence Berkeley National Laboratory

Semiconductors made from graphene and boron nitride can be charge-doped using light. When the GBN heterostructure is exposed to light (green arrows), positive charges move from the graphene layer (purple) to boron nitride layer (blue). Image Credit: DOE/Lawrence Berkeley National Laboratory

The new work addresses this — via “photo-induced doping of GBN heterostructures was used to create p-n junctions and other useful doping profiles while preserving the material’s remarkably high electron mobility.”

“We’ve demonstrated that visible light can induce a robust writing and erasing of charge-doping in GBN heterostructures without sacrificing high carrier mobility,” stated research Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Physics Department. “The use of visible light gives us incredible flexibility and, unlike electrostatic gating and chemical doping, does not require multi-step fabrication processes that reduce sample quality. Additionally, different patterns can be imparted and erased at will, which was not possible with doping techniques previously used on GBN heterostructures.”

The press release from the DOE/Lawrence Berkeley National Laboratory explains why the work is important:

Graphene is a single layer of carbon atoms arranged in a hexagonal lattice. Boron nitride is a layered compound that features a similar hexagonal lattice — in fact hexagonal boron nitride is sometimes referred to as “white graphene.” Bound together by the relatively weak intermolecular attraction known as the van der Waals force, GBN heterostructures have shown high potential to serve as platforms not only for high-electron-mobility transistors, but also for optoelectronic applications, including photodetectors and photovoltaic cells. The key to future success will be the ability to dope these materials in a commercially scalable manner. The photo-induced modulation doping technique developed by Wang and a large team of collaborators meets this requirement as it is comparable to the photolithography schemes widely used today for mass production in the semiconductor industry. Illumination of a GBN heterostructure even with just an incandescent lamp can modify electron-transport in the graphene layer by inducing a positive-charge distribution in the boron nitride layer that becomes fixed when the illumination is turned off.


“We’ve shown show that this photo-induced doping arises from microscopically coupled optical and electrical responses in the GBN heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene,” explained Wang. “This is analogous to the modulation doping first developed for high-quality semiconductors.”

While this modulation only seems to last for a few days when removed from light and kept in darkness, and recurring exposure to light erased the effect, the researchers don’t think that’s an issue.

“A few days of modulation doping are sufficient for many avenues of scientific inquiry, and for some device applications, the rewritability we can provide is needed more than long term stability,” he says. “For the moment, what we have is a simple technique for inhomogeneous doping in a high-mobility graphene material that opens the door to novel scientific studies and applications.”

The new findings are detailed in a paper published in the journal Nature Nanotechnology.

In related news, a new rapid-synthesis technique for the production of high-quality, large-area Bernal stacked bilayer graphene films was recently developed by researchers at the University of California–Santa Barbara. The researchers think that that new technique should create new possibilities in the fields of digital electronics and transparent conductors.

If you’re a graphene addict, be sure to scroll through our graphene archives. Also note that commercial graphene production has reportedly begun in Poland.

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.



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