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.