Investigation of Structural and Thermoelectric Properties of Bismuth Selenide Thin Films

Thermoelectric material with high performance and low cost is the basic need of today. Bismuth selenide is a thermoelectric material. A set of bismuth selenide thin films having different stoichiometry ratios varying Bi/Se ratio from 0.123 to 0.309 have been prepared. The present work deals with the synthesis and characterization of various thin films of bismuth selenide. The thermoelectric properties of thin films were also investigated. The aim of this work is to investigate the effect of composition ratio on the structural and thermoelectric properties and to find out the best stoichiometry ratio of bismuth selenide thin films that can be used in the application of thermoelectric devices. A set of bismuth selenide thin films having different elemental compositions were prepared by employing the thermal evaporation technique. The crystal structure and elemental composition of thin films were investigated by XRD and EDAX, respectively. The roughness of films was analyzed by AFM. The thermoelectric properties of various thin films were also measured. XRD spectrum confirms the formation of phases formed in thin films which slightly matched with standard data. AFM results indicated that the surface of films was smooth and nanoparticles were generated on the surface. AFM results indicated that the surfaces of annealed thin films were smoother than as-deposited thin films. Seebeck coefficient was found negative throughout the temperature range. The power factor was also calculated by the Seebeck coefficient and results revealed the effect of composition ratio on Seebeck coefficient, electrical conductivity, and power factor. Thin films having a composition ratio of 0.182 exhibited the highest power factor. This study provides relevant basic information on the thermoelectric property of thin films, as well as presents the effect of compositional variation on thermoelectric measurements. From the application point of view in the thermoelectric devices, the best stoichiometric thin films out of four prepared thin films have been presented.