Wide bandgap semiconductor from a hidden 2D incommensurate graphene phase

TL;DR

This paper reveals that a previously misunderstood buffer layer of graphene on SiC is in an incommensurate phase, which explains its semiconducting properties and opens new avenues for graphene-based electronics.

Contribution

It demonstrates that the buffer graphene layer is in an incommensurate phase, resolving a long-standing contradiction and explaining its semiconducting behavior.

Findings

Buffer graphene layer is in an incommensurate structure.

Incommensurate boundaries induce semiconducting π-band character.

The structure explains the discrepancy between calculations and experiments.

Abstract

Producing a usable semiconducting form of graphene has plagued the development of graphene electronics for nearly two decades. Now that new preparation methods have become available, graphene's intrinsic properties can be measured and the search for semiconducting graphene has begun to produce results. This is the case of the first graphene "buffer" layer grown on SiC(0001) presented in this work. We show, contrary to assumptions of the last forty years, that the buffer graphene layer is not commensurate with SiC. The new modulated structure we've found resolves a long standing contradiction where ab initio calculations expect a metallic buffer, while experimentally it is found to be a semiconductor. Model calculations using the new incommensurate structure show that the semiconducting $\pi$-band character of the buffer comes from partially hybridized graphene incommensurate boundaries surrounding unperturbed graphene islands.