The nature of silver impurity atoms in antimony telluride

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Abstract
Undoped Sb2Te3 and Ag‐doped Sb2Te3 crystals are grown by a modified Bridgman method. Electrical conductivity, Seebeck coefficient, Hall constant, and reflectivity in the region of the plasma resonance frequency are measured. A quantitative analysis of the silver content in the prepared Sb2Te3 crystals is made by atomic absorption spectrometry. For the undoped Sb2Te3 crystals the free carrier concentration and the effective mass in the direction perpendicular to the c‐axis, m⟂, are calculated, using a simplified model. Using m⟂ determined and the value of the plasma resonance frequency the free carrier concentration in the Sb2Te3(Ag) crystals is calculated. According to the results obtained the Ag atoms incorporated into Sb2Te3 crystals have the character of acceptors and the addition of one Ag atom corresponds to the increase in free carrier concentration by two holes. Therefore it is assumed that silver atoms substitute antimony atoms forming thus point defects of Ag″sb with two negative charges. The defects formed by Ag dopants in Sb2Te3 are compared with those in Bi2Se3(Ag) and Bi2Te3(Ag) crystals.