Influence of oxygen partial pressure on the structural, optical and electrical properties of magnetron sputtered Zr0.7Nb0.3O2 films

Thin films of zirconium niobium oxide (Zr0.7Nb0.3O2) were deposited by DC reactive magnetron sputtering method on unheated quartz and p-silicon substrates at different oxygen partial pressures. XPS studies confirmed the presence of zirconium, niobium and oxygen associated with Zr0.7Nb0.3O2 by showing the respective core-level binding energy values. The films formed at oxygen partial pressure of 4 × 10–4 Torr were of single-phase Zr0.7Nb0.3O2 with amorphous nature. Optical band gap of the films increased from 4.19 to 4.42 eV with an increase in oxygen partial pressure from 8 × 10–5 to 4 × 10–4 Torr. The Zr0.7Nb0.3O2 films formed at 4 × 10–4 Torr were also annealed in air at different temperatures in the range from 500 to 750 °C. The films annealed at temperature 600 °C showed a weak diffraction peak of tetragonal Nb2O5 with amorphous background. Further increase in temperature to 750 °C, the films transformed to polycrystalline with tetragonal structure. Shift in the diffraction angles revealed that niobium substituted the zirconium and form Zr0.7Nb0.3O2. The band gap of the films increased from 4.64 to 4.81 eV with the increase in annealing temperature from 600 to 750 °C. Metal–oxide–semiconductor (MOS) gate capacitors with configuration Al/Zr0.7Nb0.3O2/p-Si were deposited and studied the capacitance–voltage and current–voltage characteristics. The dielectric constant of the films increased from 15 to 23 with increase in annealing temperature from 600 to 750 °C. The leakage current density of the as-deposited MOS capacitors was 2 × 10–5 A/cm2 and decreased to 4 × 10–7 A/cm2 with the increase in annealing temperature to 750 °C due to improvement in the crystallinity and decrease in defect density in the films.