Comparison of the energies of vanadium donor levels in doped SnO2 and TiO2

The positions of vanadium donor levels in doped SnO2 and TiO2 have been determined by photoemission spectroscopy. The vertical ionization energy of the V(IV) level is 0.6 eV higher in SnO2 than in TiO2. Both this difference and the greater broadening of the dopant peak in V-doped SnO2 are shown to be due to the larger relaxation energy associated with the wider band gap and lower high-frequency dielectric constant of SnO2. In both doped oxides, the adiabatic ionization energy associated with the V(IV) level defines the Fermi energy.