Effects of Surface Band Bending and Scattering on Thermoelectric Transport in Suspended Bismuth Telluride Nanoplates

Abstract

A microdevice was used to measure the in-plane thermoelectric properties of suspended bismuth telluride nanoplates from 9 to 25 nm thick. The results reveal a suppressed Seebeck coefficient together with a general trend of decreasing electrical conductivity and thermal conductivity with decreasing thickness. While the electrical conductivity of the nanoplates is still within the range reported for bulk Bi2Te3, the total thermal conductivity for nanoplates less than 20 nm thick is well below the reported bulk range. These results are explained by the presence of surface band bending and diffuse surface scattering of electrons and phonons in the nanoplates, where pronounced n-type surface band bending can yield suppressed and even negative Seebeck coefficient in unintentionally p-type doped nanoplates.

Thermoelectric transport in surface- and antimony-doped bismuth telluride nanoplates

“…It has been suggested by a recent study that the measured Bi 2 Te 3 nanoplates synthesized by a similar method were unintentionally doped. 12 Additionally, it was suggested that exposure to air resulted in n-type surface band-bending on the order of 230 meV, 12 which is in qualitative agreement with that observed byARPES. 11 In contrast to the degenerate behavior observed in the Bi 2 Te 3 samples measured in the previous work 12 and the current (Bi 1−x Sb x ) 2 Te 3 samples with x = 0.5 and higher, where the measured electrical conductivity decreases with increasing temperature, opposite temperature dependence expected for non-degenerate semiconductors was observed in the two samples with x = 0.07 and 0.25 ( Figure 3(a)).…”

“…12,15,22 Incorporation of Sb is achieved by varying the molar ratio of Bi 2 Te 3 and Sb 2 Te 3 source materials. 15 The mole fractions of Sb dopants reported here as x in (Bi 1−x Sb x ) 2 Te 3 correspond to that in the precursors.…”

“…The electrical, thermal, and thermoelectric properties of the nanoplates have been obtained with the same four-probe thermoelectric measurement method as reported previously. 12,25 The sample was first held at the maximum temperature (∼450 K) for several hours, after which the sample stage temperature was gradually lowered to each measurement temperature. Electrical contact to the nanoplate sample was obtained by electrical current annealing at ∼450 K. Transmission electron microscopy (TEM) analysis was performed after transport measurements were conducted (Figure 1(c)).…”

Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

“…The in-plane thermoelectric properties of single-and double-layer MoS 2 are calculated using the Landauer transport formalism, which is equivalent to solving the Boltzmann equation in the case of diffusive transport 26,[40][41][42][43] . Here, we will briefly describe our approach to calculate the Seebeck coefficient and electrical conductivity using the full band dispersions obtained from the first-principles density functional theory (DFT).…”

“…Here, we will briefly describe our approach to calculate the Seebeck coefficient and electrical conductivity using the full band dispersions obtained from the first-principles density functional theory (DFT). More elaborate discussion of our method can be found elsewhere 40,41 . Figure 6 shows the electronic dispersion for single-layer and double-layer MoS 2 calculated by density functional theory (DFT).…”