Effect of the donor concentration on the photoresponse of the $TiO_2$ films was discussed in terms of the variation of depletion layer width. The semiconductive and electrochemical properties of $TiO_2$ films deposited by plasma enhanced chemical vapor deposition(PECVD) method have been investigated as a function of deposition time and deposition temperature by using ac impedance and photocurrent measurements. The deposition temperatures were 150, 250 and $350\circ \!C$, and the deposition times were 1200, 2400 and 3600 s at $350\circ \!C$. AC impedance and photocurrent measurements were conducted in 0.1 M NaOH solution in the applied potential range of -1 to 1 $V_{SCE}$, respectively. Polycrystalline $TiO_2$ films were deposited on the Ti substrate by application of the PECVD method. Deposition rate of the $TiO_2$ films was determined to be 0.3㎚ $s^{-1}$. Refractive index, real permittivity and imaginary permittivity of the $TiO_2$ films increased as the deposition temperature increased. Donor concentrations of the $TiO_2$ films deposited at $150\circ \!C$, $250\circ \!C$, and $350\circ \!C$ were estimated to be $2.8 \times 10^{17}$, $3.6 \times 10^{16}$, and $3.8 \times 10^{18}cm^{-3}$, respectively. Donor concentration, real permittivity and imaginary permittivity of the $TiO_2$ films increased as the deposition time increased. With increasing donor concentration from $3.6 \times 10^{16}$ to $4 \times 10^{19}cm^{-3}$, the photocurrent increased and reached a maximum value at donor concentration of $3.3 \times 10^{19}cm^{-3}$ and then decreased.
