Effect of vacancy defect and strain on the structural, electronic and magnetic properties of carbon nitride 2D monolayers by DFTB method

Abstract

We investigate the electronic and magnetic properties of CN (C6N6, C2N, C3N and C3N4) using density functional tight-binding (DFTB) method. We find that these compounds are dynamically stable and their electronic band gaps are in the range of 0.59–3.28 eV. We show that the electronic structure is modulated by strain and the semiconducting behavior is well preserved except for C3N at +5% biaxial strain, where a transition from semiconductor to metal was observed. Under +3% biaxial strain, C3N4 undergoes a transition from an indirect (K-Γ) to a direct (Γ-Γ) band gap. Moreover, band gap of C2N transforms from direct (Γ-Γ) to indirect (M-Γ) under +4% biaxial strain. However, no change in the nature of the band gap of C6N6. Further, when the studied materials under uniaxial tensile strain, their bandgaps reduce. Our theoretical study showed that an indirect-to-direct nature transition may occur for C6N6 and for C3N4, which broadens their applications. On the other hand, magnetism is observed in all N-vacancy defected CN, which encourages its application in spintronic. Moreover, calculations of formation energies indicate that N-vacancy is energetically more favorable than C-vacancy in both C2N and C3N4. Opposite behavior found for C6N6 and C3N.