Photo-Induced Doping Tames Graphene

Doping graphene with boron nitride may be a way to tame the material, introducing a bandgap and making it useful in electronic devices. However, controlling the electrical properties of graphene boron nitride (GBN) heterostructures has been tricky.

Now Lawrence Berkeley National Laboratory researchers have developed a way to tailor GBN’s electrical properties using visible light. Samples must be kept in darkness and are “erased” through uncontrolled exposure to light. The heterostructures are “rewritable,” that is, their properties can be changed again and again through photo-induced doping. Changes last only a few days.

When a graphene boron nitride heterostructure is exposed to light (green arrows), positive charges move from the graphene layer (purple) to the boron nitride layer (blue). Courtesy of Berkeley Lab.

“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,” said Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and the University of California, Berkeley Physics Department.

“For the moment,” Wang said, “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.”

Wang’s team used photo-induced doping of GBN heterostructures to create p-n junctions and other useful doping profiles while preserving the graphene’s high electron mobility. 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.

Unlike electrostatic gating and chemical doping, the light-based method does not require multi-step fabrication processes that reduce sample quality, Wang said.

Wang said his team’s approach is similar to photolithography schemes widely used today for mass production in the semiconductor industry and is commercially scalable. Viable GBN could be used in high-electron-mobility transistors, as well as in optoelectronic applications including photodetectors and photovoltaic cells, the researchers said.

The research was funded by the U.S. Department of Energy’s Office of Science and the Office of Naval Research. It was published in Nature Nanotechnology (doi:10.1038/nnano.2014.60).