DFT insights into structural, electronic and optical characteristics of un-doped and Sc-doped GeO2 rutile

Wide-bandgap materials have shown promising potential for optoelectronic devices, due to their high transparency, excellent thermal and chemical resistance, and favorable electron mobility. In this study, density functional theory (DFT) calculations using ab initio modeling were employed to examine the structural and optoelectronic characteristics of germanium dioxide (GeO₂) in its rutile phase substituted with scandium (Sc x Ge 1−x O₂, where x = 0, 0.0416, 0.0625, 0.0832, and 0.125). The calculated formation energies are negative, indicating that these materials remain thermodynamically stable. It is observed that only the addition of the Sc dopant induces changes in the structural behavior of r-GeO₂, such as an increase in the lattice parameters. The band gap of pure r-GeO 2 is 4.112 eV at (Γ – Γ), by using the Trans-Blaha-modified Becke-Johnson (TB-mBJ) approach. This value decreases to 3.778 eV as the Sc content increases, and due to the 3d orbitals of Sc, the Fermi level shifts toward the valence band, introducing holes, which leads to p-type conduction. The partial density of states (PDOS) clearly shows that the Sc-3d states are induced by the replacement of Ge with Sc, resulting in a reduction of the bandgap. The optical spectra, including the real and imaginary parts, light absorption, optical reflectivity, conductivity, refractive index, extinction coefficient, and energy loss spectrum, were studied. Furthermore, these optical properties are improved after doping with scandium compared to those of pure r-GeO₂. On the other hand, due to the high optical conductivity and absorption in the UV region, this demonstrates that Sc-doped r-GeO₂ is an interesting candidate for advanced optoelectronic devices and UV detection.