DETERMINATION OF ENERGY-DISTRIBUTION OF DONOR LEVELS IN ANODICALLY PASSIVATING TIO2 FILM

The present work is concerned with determination of energy distributio n of donor levels by analysing a.c. impedance response from the anodic ally passivating TiO2 films, based upon a new numerical method, The fr esh and halide ion-incorporated anodic TiO2 films were galvanostatical ly prepared on titanium substrate at 10 mA cm(-2) to a formation poten tial of 50 V in deaerated 0.5 M H2SO4 solution and deaerated 0.5 M H2S O4 solution containing 0.5 M of Cl- or Br- respectively. Both a.c. imp edance and photocurrent spectra were measured from the fresh and halid e ion-doped anodic TiO2 films to quantitatively determine the frequenc y dependence of donor concentration and energy distribution of deep do nors formed by the halide ions. The new numerical method analysing the frequency dependence of donor concentration was proposed to determine the energy distribution of donor levels in the fresh and halide ion-d oped anodic TiO, films. From the analysis of a.c. impedance response o n the basis of the proposed new numerical method, it was suggested tha t donor levels are distributed continuously in the energy range of 0.5 5 to 0.67 eV below the conduction band edge, In addition, it was concl uded that the donor concentration is reduced by the halide ion incorpo ration into the fresh anodic TiO2 films in the measuring frequency ran ge of 10 to 10(3) Hz, suggesting that the doped halide ions occupy oxy gen vacancy sites and simultaneously form deep donor levels in the ban d gap of the anodic TiO2 films.