THERMOELECTRIC PROPERTIES OF SiGe WHISKERS
Background. Si1-xGex solid solution whiskers with low germanium content have maximum ratio of mobility to the phonon thermal conductivity, which is promising for thermoelectrics. Thermal conductivity of SiGe nanowires is lower than of bulk samples that is also prospective for improvement of thermoelectric figure-of-merit and development of high efficiency thermoelectric microconverters. The temperature behavior of Seebeck coefficient of Si1-xGex solid solutions whiskers in temperature range from 4.2 K to above room temperatures was studied. Peculiarities of whisker shape have been successfully used to determine their thermoelectric parameters, but these investigations were not conducted for SiGe solid solution whiskers.
Objective. The aim of the paper is study of possible influence of Si1-xGex whisker geometry on their thermoelectric parameters.
Methods. SiGe whiskers were grown by CVD method in closed bromide system. The 3ω method was used to determine the temperature dependence of the thermal conductivity of Si1-xGex (x = 0.01-0.05) whiskers in the temperature range 300-400 K. Resistance of whiskers was measured by a two-probe method. The resulting I-U characteristics of cross-shaped growths were used to determine the conductivity type of the whisker material.
Results. Seebeck coefficient and resistance was shown to increase, while thermal conductivity to decrease when the whisker diameter drops from 100 to 10 μm, that is accompanied by a rise of figure of merit (up to 0.12 at 300 K). Use of the whiskers with large obliquity leads to a small increase (of about 10-15 %) of their Seebeck coefficient.
Conclusions. Thermoelectric properties of Si1-xGex (x = 0.03) solid solution whiskers doped with B impurities to the concentrations 1⋅1017–1⋅1019 cm-3 were studied in temperature range 300-420 K. An influence of the whisker morphology, in particular their diameters and obliquity, on Seebeck coefficient, thermal conductivity and resistance was investigated.
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