Spray pyrolysis deposition of Sn_xS_y thin films

Tin sulphide (Sn_xS_y) thin films have been prepared on Pyrex glass substrates by the spray pyrolysis technique using tin chloride (SnCl₂) and n, n-dimethylthiourea (CH₃NHCSNHCH₃) as starting materials. The depositions were carried out in the range of substrate temperatures from 320 to 450 degrees C. From X-ray diffraction measurements and SEM micrographs, it is found that the values of x and y, which determine the type of deposited compound, depend on the substrate temperature. At lower substrate temperatures (320-360 degrees C), mixed phases such as Sn₂S₃ and gamma -Sn₂S₃ are present. At intermediate substrate temperatures (370-390 degrees C), the SnS phase is predominant. For substrate temperatures higher than 390 degrees C the deposited material is mainly SnO₂. The optical reflectance and transmittance of SnS were used in an iterative method to obtain the refractive index (n) and the extinction coefficient (k). These values of n and k were used to calculate the absorption coefficient ( alpha ) and the bandgap (E_G), giving the result E_G=1.27 eV. Measurements of the dark conductance ( sigma ) as a function of T were made and an activation energy of 0.54 eV was determined from the slope of a plot of ln sigma versus 1/T.