Influence of substrate temperature on the growth properties of Ag-doped SnS films deposited by sputtering method

Abstract

The Ag-doped SnS films were obtained using a sputtering technique through a sub-sequential layer-by-layer SnS–Ag–SnS–Ag… approach. The structural, optical, and electrical properties of these films deposited at 200 °C, 250 °C, 300 °C, and 350 °C were investigated at a constant Ag concentration of ∼2 at. %. The XRD, Raman, and TEM confirmed that all the diffraction planes of the Ag-doped films belonged only to the orthorhombic crystal phase of the SnS. Based on the reduction in the crystal volume and the compressive type of micro-strain, it confirmed the substitutional doping of Ag into the Sn-vacancy sites in the SnS lattice. The SIMS analysis revealed that the Ag doping into SnS has occurred through the diffusion process with an increase in Ts. The XPS analysis confirmed the presence of the Sn2+, S2−, and Ag2+ oxidation states in the Ag-doped SnS films deposited at 200 °C. The direct optical band bap decreased from 1.44 to 1.42 eV with Ag doping at 200 °C, then it increased to 1.50 eV with rise in Ts (200–350 °C). All the undoped and Ag-doped SnS films exhibited a p-type conductivity. The hole carrier concentration increased from 6.65 × 1015 cm−3 to 5.74 × 1016 cm−3 with Ag doping at 200 °C, later it increased to 1.40 × 1017 cm−3 with an increase of Ts. While the hole mobility increased from 0.34 to 7.81 cm2/V.s with Ag doping at 200 °C, then as Ts increased to 350 °C it decreased to 0.35 cm2/V.s. Finally, the Ag-doped SnS grown at 200 °C exhibited the lowest resistivity (597 Ω cm) than the undoped SnS (2771 Ω cm). The Ag-doped SnS grown at 200 °C is suitable to be used as an efficient solar material.