Effect of doping and substrate temperature on the structural and optical properties of reactive pulsed laser ablated tin oxide doped tantalum oxide thin films

5% SnO2 doped tantalum oxide (Ta2O5) films are deposited on quartz substrates at different substrate temperatures of 300 K, 773 K, 873 K and 973 K using pulsed laser deposition in an oxygen ambient of 0.002 mbar. Undoped Ta2O5 films are also deposited on quartz substrates kept at substrate temperature 973 K under the same oxygen ambient using PLD. The films are characterized using GIXRD, AFM, FTIR, micro-Raman and UV-visible spectroscopy. Undoped films show an amorphous nature even at a substrate temperature of 973 K, whereas, SnO2 doped films show crystalline nature even for deposition at 300 K. As far as our knowledge goes, this is the first report of crystalline Ta2O5 films deposited at room temperature. The average size of the crystallites calculated using the Debye-Scherrer formula, shows that the size of the crystallite decreases with increase in substrate temperature. FTIR and micro-Raman spectroscopic analysis reveals the presence of Ta-O-Ta, O-Ta and O-Ta-O vibrational bands in the films. Raman analysis indicates that the addition of SnO2 suppresses the bond formation and changes the magnitude of bonds in Ta2O5. AFM patterns reveal the formation of Ta2O5 nanorods of diameter about 100 nm for the doped film deposited at 973 K. Optical transmittance of the films is found to be sensitive to substrate temperature as well as to the presence of SnO2. A blue shift in the band-gap of the doped films is observed. The decrease of band-gap with decrease of particle size observed for SnO2 doped films can be due to a band-bending effect. The transmittance of the films is found to depend on SnO2 doping and substrate temperature.