The electronic structure of bilayer MoSe2 of AB and AA stacking order under various external electric field and biaxial strain values

Abstract

Two-dimensional (2D) Materials are crystalline materials consist of a single layer of carbon atoms with thickness of few nanometers or lower. 2D materials having various properties such as high carrier mobilities, excellent conductivity, mechanical flexibility, good thermal conductivity and high optical and Ultraviolet (UV) adsorption. In MoSe2 (Molybdenum diselenide), the ‘Mo’ atoms occupy one type of sub-lattices of the hexagonal sheet and atoms of ‘Se’ occupy the others. Chemical component in MoSe2 (Ratio) is Mo: Se is equal to 1:2, the sub-lattice layer of ‘Mo’ is sandwiched between two nearby ‘Se’ sub-lattice layers. MoSe2, a transition metal dichalcogenides (TMDCs), has gained considerable attention later on for various applications in optoelectronic systems, electrochemical and photocatalytic. In this work, we analyzed the effect of external electric field and biaxial strain on the electronic structures of AB and AA stacking bilayer (BL) MoSe2 by using the density functional theory (DFT) calculations. Here we demonstrate an approach that the van der Waals (vdW) homo bilayer built by two monolayer MoSe2 has a well-controlled electronic property with applied E-field. Results show that AB stacking bilayer MoSe2 has an indirect band structure with the gap value of 1.09 eV whereas, the AA stacking bilayer MoSe2 has an indirect band structure with the gap value of 1.25 eV. The band gap of AB stacking bilayer MoSe2 decreases monotonically from the maximum (1.09 eV) at 0.0 V/Å to 0 eV at 2.8 V/Å in both, positive and negative direction along the z-axis. So, AB stacking bilayer MoSe2 have been shown to have vastly different electronic behavior, ranging from semiconductor material to metallic material, when we applied external Electric field. On other side for AA stacking bilayer MoSe2, bandgap decreases from the maximum (1.25 eV) at 0.0 V/Å to 0 eV at 2.2 V/Å in both, positive and negative direction along the z-axis. That means AA stacking bilayer MoSe2 have been also shown different electronic behavior, ranging from semiconductor material to metallic material. Recent theoretical and experimental investigations have demonstrated flexible control over their electronic states via application of external strains, such as uniaxial strain and biaxial strain. Here, we determined that the critical biaxial strain range within the bandgap of AB and AA stacking MoSe2 BL remains indirect upon application of ε from +7% to -7% (for AB) and +6% to -6% (for AA). Also, we have compared the rate of bandgap tunability of MoSe2 BL for all possible bandgap transition routes. We strongly believe that results of this analysis will help possible applications and modeling based on MoSe2 BL for future integrated electronic and optoelectronic device applications.