Strain-tunable electrical, optical and mechanical properties of Janus-MoSTe/MoTe₂ heterostructures based on first-principles calculations

Abstract This study combines density functional theory (DFT) calculations with systematic analysis to reveal the unique properties of a novel 2D Janus MoSTe/MoTe 2 heterostructure. The most stable configuration is identified as an AD-stacked heterojunction with an interlayer spacing of 6.73 Å, supported by minimal binding energy (−2.24 meV Å −1 ) and validated through phonon dispersion spectra and molecular dynamics simulations. The heterojunction exhibits a type-II band alignment with a 0.39 eV direct bandgap, where electrons are transferred from the MoSTe side to the MoTe 2 side at the interlayer position, creating a built-in electric field. That enhances electron–hole separation efficiency—a critical feature for optoelectronic applications. Optical calculations demonstrate strong ultraviolet absorption with a peak coefficient of 12.8 μm −1 at 5.4 eV, it has excellent performance and is expected to become a promising candidate for ultraviolet photodetectors. Notably, the system displays exceptional strain sensitivity: compressive strain (−2%) induces a reversible type-II to type-I transition, while 2% tensile strain triggers a semiconductor-to-metal transition, evolving into a Dirac-cone-like band structure at 4% tensile strain. Mechanically, the heterojunction shows anisotropic flexibility, coupled with a Poisson’s ratio of 0.36 that decreases sharply under strain, indicating tunable mechanical response. Combined with its robust UV absorption (12.8 μm −1 at 5.4 eV), moderate visible-light transmittance, and strain-mediated electronic transitions, these properties establish the Janus MoSTe/MoTe 2 heterostructure as a highly adaptable material for next-generation flexible optoelectronics.