Bandgap engineering and enhanced stability in Pt-doped ZnO for spintronic applications: A DFT study

This study presents a comprehensive investigation of the electronic, magnetic, and structural properties of platinum (Pt)-doped zinc oxide (ZnO) using first-principles calculations based on density functional theory (DFT) and the DFT+U approach. The inclusion of on-site Coulomb interactions via DFT+U offers a more accurate description of the localized Zn 3d orbitals, effectively capturing electron correlation effects. Pt substitution is found to enhance the thermodynamic stability of the ZnO lattice, as evidenced by negative formation energies and energetically favorable defect configurations. The electronic density of states at the Fermi level, N(E_F), was evaluated for various magnetic configurations. In the non-magnetic state, N(E_F) values of 6.36 and 2.17 states/eV were obtained for 12.5% and 50% Pt-doping, respectively, indicating a suppression of electronic states near the Fermi level with increasing Pt content. In the ferromagnetic configuration, this value decreased further to 0.392 states/eV, highlighting the influence of spin polarization. Antiferromagnetic calculations yielded a lower N(E_F) of 0.2945 states/eV at 25% doping, suggesting a tendency toward enhanced metallicity under magnetic ordering. Band structure calculations revealed that Pt doping enables effective bandgap modulation. While pristine ZnO exhibited a bandgap of 1.80 eV within standard DFT, the DFT+U method increased this to 2.81 eV, in closer agreement with the experimental value of 3.34 eV. Density of states (DOS) analysis confirmed that Zn states dominate the conduction band near the Fermi level, while the oxygen contribution remains minimal. The phonon dispersion relations and phonon DOS for pristine ZnO and 50% Pt-doped ZnO reveal the dynamical stability and modifications in vibrational modes induced by Pt substitution. Furthermore, the introduction of Pt induces local magnetic moments, indicating the possibility of magnetic ordering in the host matrix. These findings underscore the potential of Pt-doped ZnO as a multifunctional material with tunable electronic and magnetic properties, suitable for future applications in spintronics and advanced semiconductor technologies.