Graphene conducts electricity well – too well, in fact, to be useful in microelectronic technology. But by sandwiching graphene between two layers of boron nitride, which also has a hexagonal pattern, a moiré pattern results. The presence of this pattern is accompanied by dramatic changes in the properties of the graphene, essentially turning what would normally be a conducting material into one with (semiconductor-like) properties that are more amenable to use in advanced microelectronics. But in order to harness this potential for industrial use, there is first a need to better understand the dynamics.
Researchers from University at Buffalo, Japan's National Institute for Materials Science and Chiba University, Chinese Academy of Sciences (CAS), Thailand's King Mongkut’s Institute of Technology Ladkrabang and Korea's Sungkyunkwan University have chosen a strategy of rapid electrical pulsing to drive carriers in graphene/hexagonal boron nitride (h-BN) heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the “Moiré bands”, they show a cyclical evolution between metallic and semiconducting states. The team's results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices.
Moiré patterns are created by layering two similar but not identical geometric designs. For over 10 years, scientists have been experimenting with the moiré pattern that emerges when a sheet of graphene is placed between two sheets of boron nitride. The resulting moiré pattern has shown fascinating effects that could improve semiconductor chips that are used to power everything from computers to cars.
“Our recent work shows that this particular sandwich of graphene and boron nitride elicits properties that are suitable for use in new technological applications,” said Jonathan Bird, PhD, professor and chair of the Department of Electrical Engineering at UB. The research was funded in part by the U.S. Department of Energy and a MURI grant from Air Force Office of Scientific Research.
This research establishes how the moiré pattern in graphene can be adapted to use in technological applications such as new types of communication devices, lasers and light-emitting diodes. “Our work demonstrated the viability of this approach, showing that the graphene/boron nitride sandwich that we are studying does indeed have the favorable properties needed for microelectronics,” said Bird.
The semiconductor chips in question are essential not just in smartphones and medical devices but also in smart-home gadgets such as dishwashers, vacuums, and home-security systems. “Modern technology relies on the semiconductor chips that form the heart of their systems and control their operation,” said Bird. “When you talk into your cell phone, it’s the chip that converts your voice to an electronic signal and transmits it to a tower.”