Electrical Properties of Pure Tellurium and Tellurium-Selenium Alloys

The resistivity and Hall coefficient of pure, single-crystals tellurium and of six single-crystal tellurium-selenium alloys, ranging from 2. 7 percent to 13. 2 percent selenium by weight, were measured over the temperature range 90^ to 550^, and a few of the samples were taken down to liquid helium temperatures. It was found that the alloys show the same double reversal in the Hall coefficient that is exhibited by pure tellurium, going from p type to n type in the general region of room temperature, and reversing back to p type at temperatures near 200^. The upper reversal temperature decreases and the forbidden band width, as obtained from the slope of the resistivity vs temperature curves, increases with increasing selenium concentration. The room temperature resistivity and lower reversal temperature do not vary monotonically with alloy concentration but a correlation among them has been found based on ideal semiconductor theory. An explanation of the anomalous Hall coefficient which considers the effect of the electron configuration and the lattice structure on the energy band picture is discussed and it is shown how this hypothesis fits the observed facts. As a further test of this theory, the effect of a hydrostatic pressure of 5000 lb/in. on the two Hall reversal temperatures was measured.