Engineering the electronic bandgaps and band edge positions in carbon-substituted 2D boron nitride: a first-principles investigation

TL;DR

This study uses first-principles calculations to explore how compositional and configurational modifications in 2D boron nitride alloys with carbon can tune their electronic bandgaps and band edge positions for potential photocatalytic applications.

Contribution

It provides a detailed analysis of how alloy composition and C atom configuration affect the electronic properties of 2D BN-C alloys, including bandgap tuning and band edge positioning.

Findings

Bandgap can be reduced to about 2 eV with moderate C substitution.

Maximum bandgap reduction occurs when C atoms are isolated.

C atom aggregation influences the bandgap through hybridization effects.

Abstract

Modification of graphene to open a robust gap in its electronic spectrum is essential for its use in field effect transistors and photochemistry applications. Inspired by recent experimental success in the preparation of homogeneous alloys of graphene and boron nitride (BN), we consider here engineering the electronic structure and bandgap of C$_{2x}$B$_{1-x}$N$_{1-x}$ alloys via both compositional and configurational modification. We start from the BN end-member, which already has a large bandgap, and then show that (a) the bandgap can in principle be reduced to about 2 eV with moderate substitution of C $(x<0.25)$; and (b) the electronic structure of C$_{2x}$B$_{1-x}$N$_{1-x}$ can be further tuned not only with composition $x$, but also with the configuration adopted by C substituents in the BN matrix. Our analysis, based on accurate screened hybrid functional calculations, provides a clear understanding of the correlation found between the bandgap and the level of aggregation of C atoms: the bandgap decreases most when the C atoms are maximally isolated, and increases with aggregation of C atoms due to the formation of bonding and anti-bonding bands associated with hybridization of occupied and empty defect states. We determine the location of valence and conduction band edges relative to vacuum and discuss the implications on the potential use of 2D C$_{2x}$B$_{1-x}$N$_{1-x}$ alloys in photocatalytic applications. Finally, we assess the thermodynamic limitations on the formation of these alloys using a cluster expansion model derived from first-principles.