Formation of thallium antimony sulfide and thallium bismuth sulfide thin films by heating chemically deposited multi-layer thin films

摘要

Antimony sulfide (Sb_2S_3) and bismuth sulfide (Bi_2S_3) thin films of 200 nm thickness each were deposited from aqueous baths on glass substrates. Subsequently, thin films of thallium sulfide (T1_2S) with thickness around 120 nm were deposited on to these films from a bath containing thallium nitrate, sodium citrate, sodium hydroxide and thiourea. The multilayer films of Sb_2S_3-Tl_2S, Bi_2S_3-Tl_2S and Bi_2S_3-Sb_2S_3-Tl_2S, thus produced, were heated in a nitrogen atmosphere around 300℃. XRD studies confirmed the formation of TlSbS_2, TlBiS_2, Tl_4Bi_2S_5 and TlSb_3S_5 compounds. Optical band gaps of these materials are 1.85 eV (TlSbS_2), 0.15 eV (TlBiS_2), and about 1 eV for the composite film (Tl_4Bi_2S_5 + TlSb_3S_5). In the visible spectral region, the optical absorption coefficients of these materials are about 10~5 cm~(-1). Values of dark conductivity are 10~(-7) Ω~(-1)cm~(-1) (TlSbS_2), 10~(-4) Ω~(-1)cm~(-1) forTlBiS_2 and 10~(-6) Ω~(-1)cm~(-1) for the composite film. All the films are photoconductive.