Researchers from Berkeley Lab and the University of California (UC) Berkeley developed a method to open a bandgap in a graphene boron-nitride (GBN) heterostructure using visible light. Using this so called "photo-induced doping" of the GBN the researchers created pn junctions and other useful doping profiles while preserving the material’s remarkably high electron mobility.
Using visible light is very promising as this technique is very flexible and (unlike electrostatic gating and chemical doping) does not require multi-step fabrication processes that reduce the graphene's quality. Using this method, one can make and erase different patterns easily.
The idea behind this doping technology is that when light hits the BN layer, it induces a positive-charge distribution that becomes fixed when the illumination is turned off. The researchers showed 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. They say that this is analogous to the modulation doping first developed for high-quality semiconductors.
Earlier this month, researchers from the University of Manchester demonstrated that when growing graphene on a hexagonal BN, small changes in the crystal structure can open a band-gap in the graphene.