Effect of vacuum annealing temperature on structural, morphological and optical properties of In2S3:Zn films deposited by spray pyrolysis

Zinc-doped In2S3 thin films have been deposited by spray pyrolysis method at 350 A degrees C on glass substrates with ITO contacts. The samples were sealed under vacuum (10(-3) Torr) into a Pyrex tube and then annealed for 2 h at temperatures ranging from 300 to 450 A degrees C with a step of 50 A degrees C. The effect of the annealing temperature (T-a) on structural, morphological and optical properties of the In2S3 films was studied. The films, annealed at T-a aecurrency sign 300 A degrees C, result in films that consist of tetragonal beta-In2S3 phase with (220) preferential orientation, while for films annealed at T-a > 300 A degrees C, a structural transition from tetragonal to cubic beta-In2S3 occurs with (400) preferential orientation. The film grain size decreases from 42 to 33 nm. The surface morphology analysis reveals that the films annealed at 300 A degrees C present an average roughness of 40 nm. The optical band gap is found to be direct and it decreases with the increase of annealing temperature. A higher optical transmittance of 80 % is obtained at T-a = 350 A degrees C.