Structural, optical and electrical properties of chemically deposited silver sulfide thin films

Ag 2 S thin films of 90–300 nm thickness were deposited in 3–8 h at 60–70 °C on glass substrates from a chemical bath containing silver nitrate, sodium thiosulfate and dimethylthiourea (DMTU) or tetramethylthiourea (TMTU). The glass substrates used for this purpose were previously immersed in a chemical deposition bath to deposit a ZnS thin film of 40 nm thickness in the case of the bath with DMTU or subjected to a pretreatment in a methanol solution of 3-(trimethoxysilyl)propyl methacrylate for deposition from the TMTU bath. Thin film yield is >40% for the TMTU bath, when the deposition produces 60 nm films at a substrate separation of 0.4 mm, and is about 30% for film thicknesses of 90–300 nm for both baths at a substrate separation of 1–5 mm. X-ray diffraction patterns similar to that of the mineral acanthite (Ag 2 S) are observed in the case of the films heated in nitrogen at temperatures 100–200 °C; heating at 300–400 °C leads to freezing-in of the high temperature phase, argentite. Films annealed at 300 °C possess a direct (forbidden) optical band gap of about 1.0 eV. Typical electrical conductivity of the films is 10 −3 (Ω cm) −1 . A photosensitivity of approximately 100 is observed in films annealed at 200 °C, under an intensity of illumination 2 kW m −2 from a tungsten halogen lamp. Mobility–lifetime product is of the order of 10 −5 cm 2 V −1 , which suggests a free carrier lifetime of about 0.1 µs.