Optical properties of porous chalcogenide films for sensor application

The object of the present work is investigation of the optical properties of obliquely deposited thin films from As - S - Ge system. Aiming to obtain high porous coatings the deposition rate was varied in the range of 0.05-10 nm/s. The conditions for deposition of thin As - S - Ge films with columnar structure and high porosity were established. The role of the actual deposition conditions on the optical properties is examined. The optical constants (refractive index, n and absorption coefficient, alpha) and thickness, d as well as the optical band gap, E-g, and slope parameter B in dependence of the deposition angle and rate are determined from specrophotometric measurements in the spectral range 400-2000 nm applying the Swanepoel's envelope method and Tauc's procedure. Increasing of the value of n from 2.40 to 1.83 for thin film with composition As10Ge30S60 with increasing deposition angle from 0 degrees to 75 degrees is observed. The possibility of using the thin films for optical sensing of SO2 and H2S was examined. Reversible changes of the refractive index, Delta n = 0.015 were observed as a consequence of treatment virgin - exposure to H2SO4 vapors- annealing at 120 degrees C.