PNNL

Abstract

We have examined the effect of V doping on the electronic and optical properties of hematite (a-Fe2O3) by means of a-(Fe1-xVx)2O3 (0 = x = ~0.5) epitaxial films and theoretical modeling. The conductivity is enhanced by several orders of magnitude as x is increased, and this enhancement is manifested in x-ray photoelectron spectra by a growing Doniach-Sunjic tail on the O 1s peak, as well as by increasing intensity at the Fermi level in valence band spectra. Optical absorption shows a reduction in direct band gap by as much as 0.64 eV for x = 0.53 (Eg = 1.46 eV) relative to that of a-Fe2O3 (Eg = 2.10 eV). Detailed understanding of the character of the optical transitions in the alloys is achieved using first-principles calculations of the ground and excited states. These calculations reveal that V doping results in localized, occupied V 3d states which are hybridized with Fe states and located at approximately mid-gap in a Fe2O3. The lowest energy transitions involve electronic excitations from occupied V 3d orbitals to unoccupied Fe 3d* orbitals.