In the present work, variation in donor distribution in the anodically passivating $TiO_2$ film has been investigated by using ac-impedance spectroscopy and photocurrent measurement as a function of film thickness and halide ion($Cl^-$ and $Br^-$) incorporation. Also, SIMS(secondary ion mass spectrometry) depth profiling was performed on the halide ion incorporated $TiO_2$ film. Undoped and halide ion-doped anodic $TiO_2$ films were galvanostatically prepared on Ti metal in aqueous 0.5 M $H_2SO_4$ solution and aqueous 0.5 M $H_2SO_4$ solution containing 0.5 M halide ion, respectively by application of a current density of 10 mA/㎠ until the formation voltages of 30, 50 and 70 V were reached. Ac-impedance measurements were performed on the anodic $TiO_2$ films in aqueous 0.1 M NaOH solution by superimposing an ac-amplitude of 10 mV on dc-potentials between -0.9 to 1.0 $V_{SCE}$ in the frequency range from 1 to $10^4$ Hz. Photocurrent measurements were performed on the anodic $TiO_2$ films in aqueous 0.1 M NaOH solution by application of a dc-potential of 1.0 $V_{SCE}$ in the incident light wavelength range from 700 to 2000 nm. The capacitance of anodic $TiO_2$ films decreased by halide ion incorporation, indicating that the incorporated halide ions decreased effective charge density in the oxide films. SIMS analysis showed that the halide ions were distributed almost uniformly across the entire anodic $TiO_2$ film and the content of the halide ions was decreased in the order of $Cl^-$ ＞ $Br^-$ ＞ $I^-$, due to ionic radii. The results obtained from frequency dependence of donor density showed that the donor density decreased by the halide ion incorporation into the anodic $TiO_2$ film. Also, the results obtained from the frequency dependence of donor density and photocurrent measurements showed that the incorporated halide ions formed deep donor levels in the anodic $TiO_2$ film.
