Influence of lattice defects on the electrical behaviour of chlorine-doped cadmium telluride crystals

Electrical properties of semi-insulating cadmium telluride single crystals have been measured. The crystals are grown using direct crystallization under a controlled vapour pressure of cadmium doped with chlorine. Temperature dependences of Hall coefficient and conductivity show the following features. The conductivity is due to the ionization of localized levels which have E0 between Esub(v) + 0.6 and Esub(v) + 0.85 eV. The concentration of centres is not higher than 1014 cm-3. The slight dependence of carrier mobility on temperature is likely to be due to the inhomogeneous distribution of charge carriers. The low content of electrically active deep centres is interpreted to be a result of interaction between lattice defects and impurities. The impurity concentration in the crystals is higher than 1017 cm-3. Chlorine provides the best conditions for such self-refinement, being the most reactive impurity of a donor type. Gamma-irradiation from 60Co changes the type of conductivity in the crystals starting with a dose as low as 1016 cm-2. (author)