Electrical properties of vitreous Tl₂Te·As₂Te₃

Combined measurements of electrical resistivity, Hall effect and thermoelectric power have been performed on vitreous Tl₂Te·As₂Te₃ as a function of temperature. The resistivity and Hall coefficient both vary exponentially with temperature in the range 125-325°K. The activation energy deduced from the slope of the resistivity curve is equal to 0.25 eV. The Hall mobility shows a slight exponential increase with increasing temperature and has a value of 0.14 cm² V^-1 sec^-1 at room temperature. Between 145 and 300°K the thermoelectric power exhibits a linear 1/T dependence, the slope being equal to 0.13 eV. In contrast to most of the other chalcogenide glasses the sign anomaly of the Hall coefficient versus the thermoelectric power is not observed in Tl₂Te·As₂Te₃; both the Hall and Seebeck coefficients are positive. Direct observation in the electron microscope of the samples investigated reveals the presence of only a few small crystallites. The optical absorption edge of the material lies at an energy of 0.62 eV at 300°K. Interpretation of the results points to the presence of localized states in the forbidden gap. The behaviour of the drift and Hall mobility indicates a hopping process of the charge carriers.