The increase in the conductivity of chalcogenide glasses by the addition of certain impurities

It is suggested that in chalcogenide glasses, elements such as Cu or Mn can have coordination number 4 and be negatively charged, and that the compensating positive charge is provided by D+ centres. The law of mass action ensures that the concentration of D-centres is then small. Under these conditions the Fermi energy is no longer pinned and the activation energy for conduction is shown to be decreased by 1/3. Similar considerations are applied to the effect of O, Cl and K on the conductivity of amorphous Se.