Spray pyrolytic deposition and characterization of SnS and SnS2 thin films

The spray pyrolysis technique is employed to prepare thin films of SnS on glass substrates and SnS2 on glass as well as fluorine doped tin oxide (FTO) coated glass substrates. The pyrolysis temperatures of SnS and SnS2 are 350 degrees C and 275 degrees C, respectively. The films are found to be n-type semiconductors. The SnS thin film is amorphous, whereas the SnS2 shows polycrystalline structure and the calculated average grain size is 115 Angstrom for SnS2 on glass and 324 Angstrom on the FTO substrate. From an analysis of the high absorption region data a direct-allowed transition at 2.44 eV has been observed for SnS2. In the optical investigations of SnS layers an non-direct-allowed transition at 1 eV is revealed. The corresponding absorption coefficients near the fundamental absorption edge are similar to 2 x 10(4) cm(-1) and 4.6 x 10(3) cm-l for SnS2 and SnS thin films. The room temperature dark conductivity of SnS is of the order of 10(-3) Omega(-1) cm(-1) and 10(-4)-10(-3) Omega(-1) cm(-1) for SnS2 films. The corresponding photoconductivity values of SnS, SnS2 on glass and SnS2 on FTO are ten, four and two times higher than the dark conductivity.