Pulsed laser deposition of tantalum pentoxide film

We report thin tantalum pentoxide (Ta2O5) films grown on quartz and silicon substrates by the pulsed laser deposition (PLD) technique employing a Nd:Y AG laser (wavelength lambda = 532 nm) in various O-2 gas environments. The effect of oxygen pressure, substrate temperature, and annealing under UV ir radiation using a 172-nm excimer lamp on the properties of the grown films has been studied. The optical properties determined by UV spectrophotometry were also found to be a sensitive function of oxygen pressure in the chamb er. At an O-2 pressure of 0.2 mbar and deposition temperatures between 400 and 500 degrees C, the refractive index of the films was around 2.18 which is very close to the bulk Ta2O5 value of 2.2, and an optical transmittance around 90% in the visible region of the spectrum was obtained. X-ray diffra ction measurements showed that the as-deposited films were amorphous at tem peratures below 500 degrees C and possessed an orthorhombic (beta-Ta2O5) cr ystal structure at temperatures above 600 degrees C. The most significant r esult of the present study was that oxygen pressure could be used to contro l the composition and modulate optical band gap of the films. It was also f ound that UV annealing can significantly improve the optical and electrical properties of the films deposited at low oxygen pressures (< 0.1 mbar).