Development of a multi-space constrained density functional theory approach and its application to graphene-based vertical transistors

We have been developing a multi-space-constrained density functional theory approach for the first-principles calculations of nano-scale junctions subjected to non-equilibrium conditions and charge transport through them [1,2]. In this presentation, we apply the method to vertically-stacked graphene/hexagonal boron nitride (hBN)/graphene Van der Waals heterostructures in the context of tunneling transistor applications. Bias-dependent changes in energy level alignment, wavefunction hybridization, and current are extracted. In particular, we compare quantum transport properties of single-layer (graphene) and infinite (graphite) electrode limits on the same ground, which is not possible within the traditional non-equilibrium Green function formalism. The effects of point defects within hBN on the current-voltage characteristics will be also discussed. [1] Kim, H. S. and Kim, Y.-H. Bulletin of the American Physical Society \textbf{60}, BAPS.2015.MAR.T23.15. [2] Kim, H. S. and Kim, Y.-H. Bulletin of the American Physical Society \textbf{61}, BAPS.2016.MAR.K31.5.