First-principles study on the influence of tensile deformation on the optoelectronic properties of the F-HfSe₂ system

Context

Within the framework of first-principles density functional theory, this study investigates the impacts of doping and tensile deformation on the electronic and optical properties of HfSe₂. The research reveals that, after being doped with halogen elements, HfSe₂ undergoes a transition from a semiconductor to a metal, enhancing the electrical conductivity of the X-HfSe₂ systems (where X represents F, Cl, Br, or I). Among them, F-HfSe₂ exhibits the lowest formation energy and is thus selected as the research object for tensile deformation studies. The study demonstrates that, as the tensile strain increases, the energy band values of F-HfSe₂ increase linearly, enabling effective regulation of its band structure. The density of states indicates that the main contributions come from the 6d orbitals of Hf and the 4p orbitals of Se, with the F atoms contributing minimally. F atoms primarily regulate the energy bands through charge transfer processes. Optically, tensile strain enhances the light-absorbing capacity of F-HfSe₂ and induces a redshift, making it applicable in the visible and near-infrared ranges. This is attributed to the bandgap changes caused by tensile deformation. Consequently, F-HfSe₂ holds promise as an ideal material for photodetectors.

Methods

Utilizing the CASTEP module within Materials Studio software under the framework of first-principles density functional theory (DFT), geometric optimizations and optoelectronic structure calculations were performed for both intrinsic HfSe₂ and doped systems. The GGA-PBE functional was chosen for its computational efficiency and the consistency of its calculated band structure trends with more precise HSE methods, despite its tendency to underestimate bandgaps. But rigorous convergence tests were conducted to ensure the precision and reliability of the results. Specifically, a 7 × 7 × 1 K-point grid was selected for Brillouin Zone sampling after repeated testing, and the plane-wave cutoff energy was set at 600 eV. Energy convergence per atom was set at 1.0 × 10⁻⁵ eV, force convergence at 0.03 eV/Å, with stress and displacement limits at 0.05 GPa and 0.01 Å, respectively. A vacuum spacing of 20 Å was implemented to prevent interactions between periodically replicated units.