Possible negative correlation between electrical and thermal conductivity in p-doped WSe₂ single crystal

Abstract

The materials with high electrical conductivity σ and low thermal conductivity κ are the driving force for an efficient thermoelectric device. In general, electrical and thermal conductivity cannot be controlled independently as both electron and phonon participate in transport processes. Two dimensional layered materials are one such kind where van der Waals inter-layer interaction and covalent intra-layer bond favours strong phonon mediated electronic interaction. Here, we report that the substitutional p-type doping of WSe2 demonstrate negative correlation between σ and κ at wide temperature range from 5–300 K. Nominal 0.5% Nb doping of WSe2 (WSe2:Nb) increases the electrical conductivity by an order of magnitude and suppresses the thermal conductivity by the same magnitude. The formation of impurity band at close proximity (0.2 meV) of valance band display large delocalized carrier density and temperature independent mobility as compared to the undoped sample. Simultaneously, the strong delocalization of degenerate band impurity is also found to lower the thermal conductivity to 6 W m−1 K−1 at 300 K.

Synergistic Effect of Phonon Localization and Band Convergence in a WSe2–WTe2 Superlattice Leads to High Thermoelectric Performance

“…At room temperature, WSe 2 exhibits a σ of 0.01 S/m, whereas the superlattice displays an elevated value of 0.39 S/m, attributed to its four times higher mobility in comparison to WSe 2 . Notably, the calculated electrical conductivity of WSe 2 at 600 K, 70.85 S/m, with a calculated carrier concentration of 10 19 cm –3 , closely aligns with experimental findings (80 S/m) . In both materials, the conductivity of electrons surpasses that of holes, which is attributed to distinct curvatures of valence and conduction bands near the Fermi level.…”

Tungsten dichalcogenide WS2xSe2−2x films via single source precursor low-pressure CVD and their (thermo-)electric properties

“…It can be observed that all four films feature high carrier concentrations in the order of 10 18 to 10 20 cm -3 . These are significantly larger than those typically reported for TMDCs 41,43 and contribute to the high conductivities measured for the films. Such high carrier concentration is likely due to the formation of vacancies at the chalcogenide site on Please do not adjust margins Please do not adjust margins the crystallite surface.…”

“…63 In this work, despite the films all being found to be in the 2H coordination (illustrated by the XRD and the Raman spectra), all films yielded a strikingly high electrical conductivity when compared to literature. 41,64–66…”

“…63 In this work, despite the films all being found to be in the 2H coordination (illustrated by the XRD and the Raman spectra), all films yielded a strikingly high electrical conductivity when compared to literature. 41,[64][65][66] The 2H coordination would also suggest that the films will display semiconducting behaviour which is intrinsically temperature dependent due to the promotion of charge carriers to the conduction band upon absorption of thermal energy. For thermally activated conduction in semiconducting materials, the electrical conductivity ( ) can 𝝈 be expressed by the relation shown in Equation (1).…”

“…Moreover, electrical characterisation on the as-deposited WS 2x Se 2-2x (0 ≤ x ≤ 1) thin films reveal high electrical conductivities with an increase of several orders in carrier concentration when compared to literature. [41][42][43] This high conductivity is likely related to the substantial number of Se and S vacancies within the films. Such high conductivity can be tuned via an annealing process to reduce the vacancy concentration.…”