Effects of the post-annealing ambience on the microstructure and optical properties of tantalum oxide films prepared by pulsed laser deposition

Tantalum oxide films were synthesized by pulsed laser deposition (PLD). The influences of annealing temperatures and oxygen pressures on the crystalline, morphological and optical properties were investigated. Experimental results indicate that annealed film became crystallized in orthorhombic structure at 700 °C. The root-mean-square (RMS) roughness of the film became higher with the increase of annealing temperature. The transmittance and the optical band gap of the film increased with the increase of annealing temperature and the increase of annealing oxygen pressure. In addition and interestingly, crystallinity led to a decrease of transparency due to the increase of scattering losses, which resulted from the polycrystalline structure and the increase of RMS roughness. At the optimized ambience of 600 °C and 20 Pa, the transmittance of the annealed film achieved about 93% (the transmittance of bare substrate) at its peak values. And its optical band gap was 4.18 eV, which was close to the theoretical value of 4.2 eV.