Tuning Rashba Spin Splitting Strength and Photocatalytic Activity Through Van der Waals Heterostructures

Recently, Janus two-dimensional (2D) materials have attracted much interest due to possessing unique properties caused by the lack of inversion symmetry. In this work, we study the structural, vibrational, Rashba spin splitting, and photocatalytic properties of Janus SbXBr (X = S, Se) monolayer and their van der Waals heterostructures with different stacking. The inclusion of spin-orbit coupling (SOC) lifts spin degeneracy which exhibits Rashba splitting at the high symmetry Γ point in the conduction band and the valence band, respectively. The strength of Rashba splitting is obtained more in vdW heterostructures. All structures are found in indirect bandgap semiconductor nature with significant bandgaps. The Rashba splitting and semiconductor nature of these materials leads them to applications in spintronics, photovoltaic solar cells, and photocatalytic water splitting. The highest value of Rashba splitting is obtained to be 1.17 eVÅ. All heterostructures form Type-II band alignment which can be exploited to enhance the life of interlayer excitons. For the photocatalytic water splitting, we study the band edge position of the conduction band minimum (CBM) and the valence band maximum (VBM) with respect to vacuum level, all heterostructures fulfill the criteria of redox potential of the H₂ and O₂reactions. Additionally, we study the charge transfer between atomic layers to understand the carrier mobility across band alignment and Rashba splitting. All properties are carried out using first-principle density functional theory (DFT) as implimented in VASP with the inclusion of SOC. For more accurate bandgaps, HSE06 hybrid functional is used with and without SOC.