A region of anomalous negative capacitance has been observed with forward bias in Se-Tl Schottky evaporated layer structures. The effect, which is more prevalent in diodes with lower series resistance, is due to an inductive contribution to the impedance that is believed to arise from high-level injection of minority electrons into the bulk selenium.
Alloys of nominal composition Bi2−xSbxTe3+y were prepared in an evacuated, sealed ampule by a horizontal zone melting method. Single-crystal samples were cut from the ingots, and measurements of Seebeck coefficient, electrical conductivity, thermoelectric figure of merit (Z), and thermal conductivity (κ) were made over a temperature range of 160 to 360 °K using the Peltier–Seebeck method developed by Harman. Alloys of nominal composition Bi2−xSbxTe3.13 were found to be n type for [Formula: see text] and p type for x > 1. In alloys of high antimony content, the hole concentration was influenced very little by the amount of excess tellurium. The change of Z was studied by varying y from 0.06 to 0.26 at x equal to 0, 0.25, 1.4, 1.5, and 1.6 respectively. Optimum doping to maximize Z did not appear to be possible in a simple way over the entire range of x between 0 and 2. The temperature dependence of κ indicated that the maximum Z at x = 1.5 may be limited by an ambipolar contribution.
The effect of sample size on the measured thermoelectric figure of merit (Zm) determined by the Peltier–Seebeck or Harman method has been studied by progressively halving the area (As) and length (ls) of bismuth telluride alloy samples. Measurements were carried out with As values from 1 to 0.01 cm2, la values from 2 to 0.5 cm, and three different gauges of current leads (cross-sectional area Aw). The relative decrease of Zm was found to vary approximately as sech [Formula: see text] with Aw and ls constant, as In Aw with As and ls constant, and as T4/s2 with Aw and As constant, where T is the absolute temperature. The variation with As and Aw appears to be due to conduction along the sample leads, while the variation with ls is well accounted for by radiation to and from the sample. With 40 A.W.G. wires, the error in the measured figure of merit is estimated to be about 5% for a sample of dimensions 0.5 × 0.5 × 1 cm and around 50% for a sample of size 0.1 × 0.1 × 2 cm.
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