Structural and electrical properties of SnS2 thin films

Abstract

The effect of substrate temperature on the structural and electrical properties, phase composition, and surface morphology of tin disulfide thin (SnS2) films obtained by the close-spaced vacuum sublimation (CSS) method was studied. Scanning electrical microscope (SEM) images of the samples showed that all of the films were polycrystalline with an average grain size of 0.7e1.2 mm. The average thickness of the thin films was 1 mm. Energy dispersive spectroscopy (EDS) analysis showed that all layers had close to stoichiometric atomic composition. Namely, the concentrations of tin and sulfur were 35 and 65% respectively. X-ray diffraction (XRD) study indicated that the samples obtained at 473e723 K mostly contained hexagonal phase SnS2 with high texture along the (002) crystallographic plane. The values of the lattice constants (a and c) of SnS2 thin films increase monotonically with substrate temperature from 0.3637 to 0.3647 nm and from 0.5703 to 0.5743 nm, respectively. Investigation of the SnS2 films by Raman spectroscopy confirmed the results of XRD studies, namely that the layers have single-phase hexagonal structure of 2H polytype. Studies of the electrical properties of SnS2 thin films showed that the conductivity of the films changed from 1.8 10 4 to 10 7 (Om,cm) 1. Analysis of the IeV characteristics in the space-charge limited current (SCLC) mode made it possible to define (Et1 ¼ (0.52e0.55), Et2 ¼ (0.46e0.49), Et3 ¼ (0.43e0.45), and Et4 ¼ (0.35e0.39) eV), the localized states energy depths in the band gap of the SnS2 thin films. The concentration of these localized states exceeds 1.31 1014 сm 3. Also, from the measurements of temperature dependent conductivity, several localized states with activation energies of 0.25 and 0.26 eV states were determined.