X3N (X=C and Si) monolayers and their van der Waals Heterostructures with graphene and h-BN: Emerging tunable electronic structures by strain engineering

Using density functional theory, we explore the electronic structures of the two-dimensional (2D) C3N and Si3N, as well as C3N-based van der Waals heterostructures with graphene and h-BN. The two-dimensional (2D) C3N is demonstrated to be an indirect semiconductor with atomically flat nanostructure, while the 2D buckled Si3N exhibits metallic property. The semiconductor-metal transition can be obtained under compressive strain of -8% and tensile strain of 14% for the 2D C3N, and the metal-semiconductor transition can be achieved when 10% stretch strain is applied for the Si3N. Moreover, the C3N-BN heterojunctions with three different stackings are energetically favorable based on the formation energy analysis. The Dirac-like point of C3N is broken as the interlayer distance is decreased, and the band alignments of the C3N-BN heterojunctions are significantly affected by the external strains. In contrast, both AA-and AB-stacked C3N-graphene heterojunctions possess excellent Ohmic contact. The p-type Ohmic contact of the AA stacking can be switched to the n-type provided that the vertical distance is substantially decreased. The tunable electronic properties of the 2D C3N and the comprehensive understanding of C3N-based van der Waals heterostructures influenced by strain engineering may facilitate their practical applications for nanoelectronics and optoelectronics. (c) 2018 Published by Elsevier Ltd.