Electrical and optical properties of bismuth sulphotelluride [Bi2(S1-xTex)3] thin films prepared by arrested precipitation technique (APT)

Semiconducting bismuth sulphotelluride [Bi2(S1-xTex)3] thin films were grown by using initial ingredients bismuth triethanolamine complex, thioacetamide and sodium tellurosulphite in an aqueous alkaline medium. Thin, uniform, tightly adherent and densely packed deposits are obtained by employing arrested precipitation technique (APT). The optical absorption studies revealed that the films have high absorption coefficient with a band to band (direct) type transitions and the energy gap decreased typically from 1.62 eV for pure Bi2S3 down to 0.65 eV for pure Bi2Te3. The transition of the material is found to be band to band direct type. The electrical conductivity measurements showed increase in the conductivity with increased tellurium content (x) in the film. From TEP measurements the films showed n-type of conduction mechanism for all the samples. The thermo power is of the order of μV/K