Conductivity and thermoelectric power of trigonal Se x Te 1− x single crystals

Conductivity σ and thermoelectric power α of SeTe mixed crystals have been measured in the temperature range from 100 K up to the melting points. The activation energy of the intrinsic conductivity shows a relatively complicated dependence on alloy composition, which can be explained by a transition from the direct gap of Te to the indirect gap of Se at about 40% Se content. The extrinsic conductivity has an activation character in a large part of the system. Formally the activation energy Δ E has to be attributed to the mobility. It decreases continuously towards Te and vanishes at the high Te end. Δ E can be explained by a strongly inhomogeneous hole concentration as for trigonal Se. The density of states mass of holes has been estimated, which increases approximately linearly with Se content from 0.2 m 0 for Te to about 1.4 m 0 for Se.