Influence of post-deposition annealing on electrical and optical properties of (Ta2O5)1-x - (TiO2)x thin films, x ≤ 0.08

Tantalum (Ta) and titanium (Ti) metal targets were direct current (DC) magnetron sputtered in the oxygen environment by varying its relative areas to deposit (Ta2O5)1-x- (TiO2)x (TTOx) thin films, with x = 0, 0.03, 0.06, and 0.08, onto the boron-doped p-silicon (1 0 0) and optically polished quartz substrates, at room temperature; and were annealed at 500, 600, 700, and 800 °C, for 1.5 h. The thin films annealed at and above 600 °C show the Ta2O5 structure. The leakage current density and capacitance-voltage (C–V) characteristics were measured for TTOx, x ≤ 0.08, assisted Ag/TTOx/p-Si metal– oxide– semiconductor (MOS) structures. The leakage current density was found minimum, for the films annealed at 800 °C, for all the prepared TTOx films, x ≤ 0.08. The minimum leakage current density 1.6 × 10−8 A/cm2, at 3.5 × 105 V/cm electric field, was observed for x = 0.03, annealed at 800 °C, among the prepared compositions. The prepared TTO0.03 films, annealed at 700 °C show maximum dielectric constant 39, at 1 MHz. The optical parameters, viz., refractive index (n), extinction coefficient (k), and optical band gap (Eg) of the films, with x = 0.03, prepared on quartz substrates, were determined from their optical transmittance plots. The values of n and k of the crystalline films were observed increasing from 2.123 to 2.143, and 0.099 to 0.130, respectively, at 550 nm wavelength; and Eg decreasing from 3.95 to 3.89 eV with the increasing annealing temperature, from 600 to 800 °C. Ohmic emission, in the lower electric field; Schottky and space-charge- limited current conduction mechanisms, in the intermediate to higher electric fields, were generally envisaged from the current-voltage characteristics in the prepared Ag/TTO0.03/p-Si structures.