Stacked 2D nanoflake-structured thin films of chalcogenide SnS_xSe_(y−x) grown by spray pyrolysis: structural, optical and electrical properties

In the present work, ternary SnS_xSe_(2−x) structures were synthesized as thin films by the spray pyrolysis technique. Structural, electrical and optical properties were studied as a function of the deposition temperature. XRD and EDS results showed the presence of the SnS_xSe_(2−x) phase in the films deposited at temperatures from 300 to 400 °C. The phase SnSSe was obtained at 400 °C and at higher deposition temperatures a mixture of the SnS_xSe_(2−x) and SnS_xSe_(1−x) phases becomes present in the samples. XRD also indicated a preferential growth along the (001) direction, and this result is corroborated with SEM images where nanometric flakes with the hexagonal form corresponding to the SnS_xSe_(2−x) phase were observed. An n-type conductivity was obtained by both Hall-Van der Pauw and Seebeck measurements in the films deposited from 300 to 400 °C. For films deposited at temperatures above 400 °C, a p-type conductivity was obtained in some samples. A Seebeck coefficient as high as 603 μV/K was obtained for the sample deposited at 400 °C. Bandgap energies were obtained from the transmittance and reflectance spectra. The bandgap varied from 2.44 to 1.04 eV, yielding a value of 1.28 eV for the SnSSe sample.