Magnetron-Sputtered AgBi(S,Se)₂ Thin Films: Thermal Chalcogenization, Structural Evolution and Band-Gap Tuning

V.Pakštas1, G.Jocytė1, A.Selskienė1, R.Giraitis1, M.Franckevičius1

1Center for Physical Sciences and Technology, Sauletekio av.3, LT-10257, Lithuania

e-mail: vidas.pakstas@ftmc.lt

Silver bismuth sulfide (AgBiS₂) is a lead- and cadmium-free chalcogenide semiconductor with strong optical absorption and a band gap suitable for thin-film optoelectronic applications. In this work, AgBiS₂ and Se-containing AgBi(S,Se)₂ thin films were prepared by magnetron sputtering followed by thermal chalcogenization.

Ag and Bi metallic layers were first deposited by magnetron sputtering and then sulfurized to form AgBiS₂ coatings. The effect of the Ag/Bi layer sequence and thermal treatment conditions on the resulting films was examined. Dense AgBiS₂ coatings with a thickness of approximately 0.5 μm were obtained after sulfurization. These films were then subjected to short thermal selenization treatments to introduce Se into the AgBiS₂ layers.

Se incorporation was already observed after 1–5 min of selenization, resulting in mixed AgBi(S,Se)₂ compositions. The Se content varied through the film thickness, indicating the formation of a concentration gradient during the short selenization treatment. Increasing Se incorporation also changed the crystal structure from the cubic AgBiS₂ phase towards a hexagonal structure. The optical band gap decreased from approximately 1.1 eV for the initial AgBiS₂ films to approximately 0.8 eV for Se-containing films, extending the absorption range into the near-infrared region.

The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and optical absorption measurements. The results show that short thermal selenization can modify the composition, crystal structure, and optical band gap of magnetron-sputtered AgBiS₂ coatings. The combination of a controlled metallic precursor deposition and short-time Se treatment provides AgBi(S,Se)₂ films with band gaps in the 0.8–1.1 eV range, which is of interest for near-infrared optoelectronic applications.

We acknowledge the project funded by the Research Council of Lithuania (LMTLT), agreement No. S-MIP-25-76

REFERENCES

[1] Chalapathi U., Sangaraju S., etc. Synthesis of AgBiS2 films by sulfurizing Bi/Ag stacks for thin film photovoltaics. Optical Materials. 2024,152, 115492.

[2] Prodan J, Prudnikau A, ACS Omega, Colloidal AgBiSe2 and AgBi(S1–xSex)2 Nanocrystals with Composition-Tunable Properties Based on Bis(acyl) Selenide Precursors 2026, 11(30), 45297-45305.