Mechanism for Doping in Bi Chalcogenide Glasses

The structural environment of Bi incorporated in Ge chalcogenide glasses has been found from extended x-ray absorption fine-structure data to consist of threefold coordination. An increase by a factor of 2 in the Debye-Waller factor occurs as the carrier type changes from $p$ to $n$. A mechanism involving the suppression of positively charged structural defects, and the consequent unpinning of the Fermi level, by the formation of partially ionic Bi-chalcogen bonds is proposed to account for the doping effect.