Electrical Transport and Structural Properties of Bulk As-Te-I, As-Te-Ge, and As-Te Chalcogenide Glasses

A variety of compositions of glass in the As-Te-I, As-Te-Ge, and As-Te chalcogenide series have been prepared and structurally analyzed. The analytical techniques included x-ray powder diffraction, density determinations, and differential-scanning-calorimetry experiments. The temperature dependence of the Hall mobility, Seebeck coefficient, and dc conductivity was determined for six representative alloy compositions. The Hall mobility was found to be $n$-type, low, and activated with nearly equal activation energies in each case. The conductivity mobility was deduced from the $p$-type Seebeck coefficients and the conductivity measurements to have an activated character with a characteristic energy of 0.19 ± 0.02 eV for all the measured compositions. These results appear to be inconsistent with the familar Cohen-Fritzsche-Ovshinsky (CFO) picture for transport in amorphous semiconductors, and a new model for conduction in these glasses is proposed. This model involves the hopping of holelike small polarons between sites associated with a common As-Te structural entity which is postulated to be present in all the alloys measured here. The sign, magnitude, and temperature dependence of the dc conductivity, Seebeck coefficient, and Hall mobility are all consistent with this model.