Herein thin films of bismuth oxide are doped with iron by the thermal deposition technique under a vacuum pressure of 10–5 mbar. The doping content varied in the range of 3.0 wt.% to 13.0 wt.%. It is found that undoped and Fe-doped Bi2O3 films exhibited monoclinic structure with lattice parameters of \(a=7.9765\;\overset\circ A,\;b=7.1253\;\overset\circ A,\;c=4.5964\;\overset\circ A\) and \(\beta =102.203^\circ\) and space group \(8/Lc140\) . Fe-doping below the solubility limit (13.0 wt %) resulted in smaller crystallites, larger strains and larger defect densities. Above the solubility limits orthorhombic Fe2O3 occupied 30.6% of the total phase of Bi2O3 films. Fe-doped Bi2O3 films showed lower dielectric constant value, lower electrical conductivities and larger microwave cutoff frequencies. Analyses of the ac conductivity spectra indicated that the ac conduction is dominated by the correlated barrier hopping. The increased doping level below the solubility limit decreased the density of localized states near Fermi level and increased the correlated barrier height. It is also observed that 3.0 wt% of Fe can improve the cutoff frequency from 133 to 160 GHz. The cutoff frequency spectra of pure and doped samples displayed values that suits 6G waveguides, field effect transistors, and other high-frequency applications.
