First-Principles Insights into Interlayer Distance, Strain, and Electric Field-Modulated Electronic Properties of FeCl₃/WSi₂N₄ Heterostructures

In this work, the electronic properties of the FeCl3/WSi2N4 van der Waals heterostructure (vdWH) are investigated via first-principles calculations, emphasizing the impacts of layer spacing, in-plane strain, and external electric fields. The vdWH band structure exhibits a remarkable response to the interlayer spacing between FeCl3 and WSi2N4, with the bandgap first increasing from 0.18 eV (ΔD = 2.25 Å, where ΔD represents the interlayer distance) to a peak of 0.82 eV (ΔD = 3.368 Å) and then declining to 0.31 eV (ΔD = 4.48 Å). Meanwhile, the heterojunction shifts from type-II to type-I and then back to type-II. The bandgap increases from 0.27 eV (ε = −3%) to 1.58 eV (ε = −2%) and then decreases to 0.18 eV (ε = 4%) under in-plane strain, and the biaxial compressive strain can result in a change of the heterojunction type. Moreover, the applied electric field can also regulate the bandgap and alter the heterojunction from type-I to type-II. When the field direction is from FeCl3 to WSi2N4, the bandgap gradually increases from 0.72 eV (E = −0.4 V/Å) to 0.76 eV (E = −0.1 V/Å). Conversely, the bandgap remains nearly constant at around 0.82 eV under the reverse direction. These tunable electronic properties indicate that FeCl3/WSi2N4 vdWHs are highly adaptable and have substantial potential for future wearable devices, flexible electronics, and optoelectronic devices.