Conductor formation through phase transformation in Ti-oxide thin films

The resistance and transmittance of Ti-oxide thin films sputtered on quartz substrates were studied. The electrical and optical properties can be changed by varying the percentage of O ₂ introduced during the sputtering. The lowest resistivity for the sputtered Ti-oxide thin film was 2.30 × 10 ^-2 ω cm for 12.5% O ₂, which was obtained after annealing at 400°C in ambient oxygen. The results of x-ray photoelectron spectroscopy (XPS) curve-fitting indicate that the Ti-oxide thin film contained both Ti ₂O ₃ and TiO ₂ phases during deposition. The Ti ₂O ₃ phase was transformed into the stable TiO ₂ phase during annealing. The Ti ₂O ₃-TiO ₂ phase transformation initiated the substitution reaction. The substitution of Ti ⁴⁺ ions in the TiO ₂ phase for the Ti ³⁺ ions in the Ti ₂O ₃ phase created the free electrons. This Ti ₂O ₃-TiO ₂ phase transformation demonstrates the potential mechanism for conduction in the annealed Ti-oxide thin films. The transmittance of the annealed Ti-oxide thin films can be as high as approximately 90% at the 400 nm wavelength with the introduction of 16.5% O ₂. This result indicates that the annealed Ti-oxide thin films are excellent candidates for use as transparent conducting layers for ultraviolet (UV) or near-UV light-emitting diode (LED) devices.