The Preparation And Characterization Of Zn Doped SnS Thin Films

The Zn doped SnS thin films were prepared by vacuum co-evaporation with single source on glass substrates, to obtain good thin films by different heat treatment condition in nitrogen. The structure, surface morphology, optical and electrical properties of the film were tested by X-ray diffraction, atomic force microscope, manual profiler, X-ray photoelectron spectrum, ultraviolet-visible spectrophotometer, desktop multimeter.The experimental results showed that the film prepared by evaporation with mixed powder of Sn:S ratio to 1:0.8(at%) and heat treatment at 350℃for 40 minutes was simple orthorhombic SnS polycrystalline thin film whose space group is Pcnm(53). The film had a strong (004) preferential orientation. The SnS films with a mixed structure of simple orthorhombic and face-center orthorhombic with space group Cmcm(63) were prepared with the same ratio of Sn and S at 2wt% or 4wt% Zn doped with heat treatment at 300℃for 40 min. The surface of Zn-doped films became more compact and pores reduced. The state of Sn and S were Sn+2 and S-2 in Zn doped SnS films and un-doped SnS films. Zn in SnS thin films existed in two states for interstitials and substitutions and its chemical state was Zn+2. The surface and body element stoichiometry were:Sn:S=8.76:1, Sn:S=1.9:1 respectively in un-doped SnS thin films; Sn:S=2.95:1, Sn:S=1.38:1 respectively in 2wt% Zn doped SnS thin films and Sn:S=2.87:1, Sn:S=1.36:1 respectively in 4wt% Zn doped SnS thin films. S in SnS thin film surface suffered serious losses. Zn doped SnS in the preparation process can inhibit the loss of S to improve the film stoichiometry.Direct optical band gap of SnS films was 1.95eV. After Zn (2wt% and 4wt%) doped, the band gap narrowed, respectively,1.375eV,1.379eV, the optical absorption edge shifted to long-wave. Doping Zn can significantly improve the conductivity of SnS films. The resistivity of pure SnS thin films was 103(Ω·cm) magnitude order. The resistivity of Zn (2wt% and 4wt%) doped films with heat treatment at 300℃for 40 min, decreased 6-7 magnitude order, respectively,1.8528×10-3Ω·cm, 4.944×10-4Ω·cm. Un-doped SnS thin films were intrinsic semiconductors and Zn doped films were n-type semiconductors.