Thallium antimony sulfide and thallium bismuth sulfide thin films produced by heating chemically deposited multi-layers

Abstract

Thin films of antimony sulfide and bismuth sulfide, each about 200 nm in thickness, were deposited from aqueous baths on glass substrates. Thallium sulfide thin films were subsequently deposited on these films from a bath containing thallium nitrate, sodium citrate, sodium hydroxide and thiourea solutions. XRD studies confirmed the formation of TlSbS2 and TlBiS2, respectively, when Sb2S3–Tl2S and Bi2S3–Tl2S layers were heated in a nitrogen atmosphere at 300 °C for 1 h. When a layer of Bi2S3–Sb2S3–Tl2S was heated at 280 °C, a composite film consisting of Tl4Bi2S5 and TlSb3S5 was produced. Optical bandgaps of these materials were found to be 1.85 eV (TlSbS2), 0.15 eV (TlBiS2) and about 1 eV for the composite film (Tl4Bi2S5 + TlSb3S5). In the visible spectral region, the optical absorption coefficients of these materials are about 105 cm−1. Values of dark conductivity are 10−7 Ω−1 cm−1 (TlSbS2), 10−4 Ω−1 cm−1 (TlBiS2) and 10−6 Ω−1 cm−1 for the composite film. All the films are photoconductive.