Effect of excess tellurium on optical and thermoelectric properties of Sb2Te3 crystals

Sb₂Te₃ and Bi₂Te₃ are the most important thermoelectrics among the V₂-VI₃ compounds. Whereas the normal stoichiometric synthesis of these compounds is usually difficult due to the high vapour pressure of Te causing loss of Te: the resulting conductivity type is always p-type. In efforts to obtain the correct stoichiometry, adding higher offstoichiometric Te is frequently known to change the conductivity of Bi₂Te₃ from p- to n-type. The chapter describes a similar aspect for the case of Sb₂Te₃ with a 10 at% excess of Te, and studied its properties. The investigation of V₂ VI₃ alloys indicates that some of them are semiconductors and exhibit interesting properties for photoconductor and thermoelectric applications. Of these, the layered compounds Sb₂Te₃, Bi₂Te₃, Bi₂Se₃ possess narrow band gaps and exhibit interesting characteristics such as non-stoichiometry, possessing antisite defects and thermoelectric properties.