Effect of External Electric Fields on Defective AlN/Graphene Heterobilayer: A First-Principles Study

Graphene-based van der Waals heterobilayers play a fundamental role in the fabrication of optoelectronic, micro- and nanoelectronic, and spintronic devices. In this paper, four new stackings for the (4 × 4)-AlN/(5 × 5)-graphene denominated as AA, AA', A'B, and A'B' are investigated, using density functional theory. The results of the binding energy show that stackings AA and AA' are the most energetically favorable, and the calculations of the energy of formation and the phononic dispersion curves prove that the two stackings with and without monovacancies of Al (V_Al) and N (V_N) are structurally, thermodynamically, and dynamically stable. In addition, a study of the effect of external electric fields on the electronic and magnetic properties of the AlN/graphene heterobilayers with V_Al and V_N is undertaken, and it shows a path for modulating the magnetic properties of the AlN/graphene heterobilayers with V_Al and V_N. It was observed that without external electric fields, the heterobilayers with V_N are metallic and nonmagnetic, while those with V_Al are half-metallic and magnetic. In the presence of external electric fields within the interval [-0.2, +0.2] V/Å, it was observed that the heterobilayers with V_N maintain their metallic and nonmagnetic behavior. Conversely, heterobilayers with V_Al conserve their half-metallic character, but their total magnetization varies according to the direction of the field applied: it increases when the field is oriented in the normal positive direction to the heterobilayer and diminishes when the field is applied in the opposite direction. More precisely, it establishes a quasi-linear (AA stacking) and linear (AA' stacking) relation between the magnetization, M(E⃗), and the intensity of the applied electric field, E⃗, with magnetoelectric susceptibilities of ∼0.46 and 0.5 μ₀Å/V, respectively. From these results, it can be inferred that the AlN/graphene with V_Al in the presence of electric fields within the aforementioned range could exhibit a magnetoelectric effect, and finally, the effect of applying an electric field on the magnetic properties of the AlN/graphene heterobilayer with Al monovacancies was studied.