Optical properties of porous chalcogenide films for sensor application

Abstract

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, α) and thickness, d as well as the optical band gap, Eg, 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° to 75° is observed. The possibility of using the thin films for optical sensing of SO2 and H2S was examined. Reversible changes of the refractive index, Δn = 0.015 were observed as a consequence of treatment virgin – exposure to H2SO4 vapors– annealing at 120 °C.