Obtaining the properties of renium-based two-dimensional materials and their use in photodetector structures

This thesis presents a comparative first-principles investigation of the direction-dependent electronic, optical, and structural properties of monolayer ReS₂ and ReSe₂ materials. Within the framework of density functional theory (DFT), both PBE and HSE06 functionals were employed to compute the electronic band structures, dielectric responses, absorption spectra, infrared (IR)-active phonon modes, and X-ray diffraction (XRD) patterns of these materials. The HSE06-corrected bandgaps were found to be 1,846 eV for ReS2 and 1,628 eV for ReSe2, showing better agreement with experimental values. The calculated dielectric functions revealed significantly higher magnitudes in the x and y directions compared to the z direction, indicating strong in-plane anisotropy. The absorption coefficients reached magnitudes on the order of 10⁵–10⁶ cm⁻¹ within the visible and ultraviolet (UV) spectral ranges, demonstrating strong yet directionally dependent light–matter interactions. While the IR spectra revealed direction-specific phonon modes, the simulated XRD patterns confirmed the layered crystal structures via dominant (00l) reflections. Unlike most previous studies that focus solely on in-plane optical responses or a single compound, this work provides both a unified and comparative perspective on the anisotropic behavior of distorted 1T-phase ReX2 materials. Furthermore, the physical parameters obtained from the DFT calculations were incorporated into the SCAPS-1D simulation software to model photodetector structures with a Gr/ReX₂/PSi/p-cSi/Au configuration. Simulation results showed that both structures possess an external quantum efficiency (EQE) in the range of 85–88%, an open-circuit voltage (VOC) of 0.74–0.75 V, a short-circuit current density (JSC) of 40–43 mA/cm², a fill factor (FF) of approximately 83%, and a power conversion efficiency (PCE) exceeding 25%.