First-principles study of germanium-doped WX2 (X = S, Se) monolayers

• WX 2 and Ge-doped WX 2 (X = S, Se) crystals were synthesized via chemical vapor transport and characterized. • Ge doping transitions WX 2 monolayers from n-type to p-type with reduced bandgaps. • Strain effectively reduces the bandgap, enabling electronic property tuning. • Ge doping causes a redshift, improving visible light absorption and showing promise for applications in solar cells and photodetectors. In this work, we synthesized crystals of WX 2 and Ge-doped WX 2 (X = S, Se) using the chemical vapor transport (CVT) method and characterized them via transmission electron microscopy. Furthermore, we employed density functional theory (DFT), to investigate the change in the electronic and optical properties of monolayer WX 2 with Ge doping concentration. We systematically examined the modulation of electronic properties of the pure WX 2 (X = S, Se) and Ge-doped WX 2 monolayer (ML) systems under biaxial strain by analyzing band structures and densities of states. Additionally, we analyzed the optical properties, including real and imaginary parts of the dielectric function, energy loss function, reflectivity spectra, refraction, and absorption.