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 degrees C, for 1.5 h. The thin films annealed at and above 600 degrees 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 degrees C, for all the prepared TTOx films, x < 0.08. The minimum leakage current density 1.6 x 10-8 A/cm2, at 3.5 x 105 V/cm electric field, was observed for x = 0.03, annealed at 800 degrees C, among the prepared compositions. The prepared TTO0.03 films, annealed at 700 degrees 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 degrees 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.

Automated summary

Tantalum and titanium thin films were deposited by DC magnetron sputtering in varying oxygen environments, with annealing temperatures affecting the structure and properties. Films annealed at 800°C exhibited the lowest leakage current density, while TTO0.03 films annealed at 700°C showed the highest dielectric constant. The optical parameters of the films were evaluated, showing changes in refractive index, extinction coefficient, and optical band gap with increasing annealing temperature. Different current conduction mechanisms were observed in the prepared metal-oxide-semiconductor structures.