Diameter dependent thermoelectric properties of individual SnTe nanowires

Abstract

The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ∼218 to ∼913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25-300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ∼913 nm to ∼218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.

Surface oxidation and thermoelectric properties of indium-doped tin telluride nanowires

“…67 The positive sign of S confirms the p-type nature of the majority charge carriers. The thermopower decreases monotonically with the decrease of temperature and shows no bipolar effect.…”

“…67 The metallic behavior in SnTe is attributed to degenerate doping by native Sn vacancies which act as acceptors (or p-type dopants). The density of Sn vacancies is estimated to be on the order of 10 20 cm -3 (or 1%), 31,67 comparable to the indium dopant concentration in the core of the wire.…”

“…[66][67][68][69][70] As shown in Figure 7c, the κ at 300 K is 2. 76 The lattice thermal conductivity κ L is then determined by subtracting the total thermal conductivity by the electronic thermal conductivity.…”

“…The non-monotonic relationship between κ L and temperature may be due to the increase of phonon density upon warming at lower temperatures and the enhancement of umklapp phonon-phonon scattering at higher temperatures. 67 The ZT was finally calculated and plotted as a function of temperature in Figure 7d. At 300 K, the ZT of our nanowire is 0.07, which is comparable to that of Indoped SnTe polycrystalline samples (~ 0.08 -0.09) 1 but higher than that of undoped SnTe nanowires (~0.0379).…”

“…The thermal conductivity was measured using a self-heating method: by applying a large current through electrodes A and D, a voltage between B and C was measured and the resistance was calculated. [66][67][68][69][70] The average temperature increase of the nanowire ∆T M was then determined from the resistance change (a linear temperature dependence is assumed in a 10 K interval). The thermal conductivity can be calculated based on = 2 /(12Δ ), where I is the current, R is the resistance, l is the channel length, and A is the cross section of the nanowire.…”