Comparative analysis of strain engineering on the electronic properties of homogenous and heterostructure bilayers of MoX₂ (X = S, Se, Te)

In this work, for the first time, the comparative electronic properties of homogenous and van der Waals (vdW) heterostructure bilayers of Molybdenum Dichalcogenides, MoX₂ (X = S, Se, Te) is investigated using first-principle calculations with the emphasis on their response to applied biaxial mechanical strain. The dynamical, thermal, and energetical stability of the vdW bilayers are assessed in detail. Next, a comprehensive analysis of energy band structure with the atomic orbital projections of band edges has been performed for individual bilayers. In this context, the energy of different conduction and valence band edges are studied within a range of 5% biaxial compressive (BC) to 5% biaxial tensile (BT) strain. The applied strain-dependent band edge energy modulations are extensively analysed based on the change in structural properties and thereby the strength of in-plane and interlayer atomic orbital couplings. The analysis is further extended to correlate the variations in energy bandgaps and density of states (DOS) in different bilayers with applied strain. The results indicate that, unlike homogenous bilayers, the vdW bilayers demonstrate distinct electronic properties in their relaxed configuration. Specifically, the MoSe₂/MoTe₂, MoS₂/MoSe₂, and MoS₂/MoTe₂ exhibit small direct bandgap, moderate indirect bandgap, and metallic/semimetallic nature, respectively. Furthermore, distinctly different modulations in conduction band minima (CBM) and valence band maxima (VBM) positions in the Brillouin zone are observed with applied strain for individual vdW bilayers in contrast to almost similar nature of variations in CBM/VBM positions of homogenous bilayers. This leads to characteristic nonlinear variations in energy bandgap and distinct DOS modulations for individual vdW bilayers under applied strain. The key findings indicate that the suitably strained VdW bilayer MoX₂ are highly promising materials for a plethora of electronic and optoelectronic applications.