| Tantalum and niobium oxide optical thin films were prepared at room temperature by Plasma-Enhanced Chemical Vapor Deposition (PECVD) using different modes of deposition (RF, MW and MW/RF) using tantalum and niobium pentaethoxide (M(OC2H5)5) precursors. They were then tested for their stability.;The evolution of the films' optical and microstructural properties as a result of annealing was studied over a broad temperature range from room temperature up to 900°C. The as-deposited films were amorphous, their refractive index, n, and extinction coefficient, k, at 550 nm were n = 2.13 and k < 10-4 for Ta2O5, and n = 2.24 and k < 10-4 for Nb2O 5. The films contained a small amount of residual carbon (∼ 2--6 at. %) bonded mostly to oxygen. During annealing, the onset of crystallization was observed at approximately TC = 650°C for Ta2O5 and at TC = 450°C for Nb2O5. Upon annealing close to T 1 (300°C for Nb2O5 and 400°C for Ta 2O5), n at 550 nm decreased by less than 1%. During annealing, a phase transition from the δ- (hexagonal) phase to the L- (orthorhombic) phase was observed between 800°C and 900°C for Ta2O5, and between 600°C and 700°C for Nb2O5. (Abstract shortened by UMI.). |
