Thermal conductivity for p-(Bi, Sb)$_{2}$Te$_{3}$ films of topological insulators

TL;DR

This study investigates the temperature-dependent thermal conductivities of topological insulator films p-(Bi, Sb)$_{2}$Te$_{3}$, revealing how grain interfaces and defects influence phonon and electron transport.

Contribution

It provides new insights into the thermal transport mechanisms in topological insulator films, highlighting the effects of deposition methods and microstructure on thermal conductivity.

Findings

Grain interfaces significantly reduce lattice thermal conductivity.

Electronic thermal conductivity increases at low temperatures due to defect scattering.

Morphology correlates with thermal conductivity variations.

Abstract

The temperature dependences of the total, crystal lattice and electronic thermal conductivities were investigated in films of topological insulators p-Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ and p-Bi$_{2}$Te$_{3}$ formed by discrete and thermal evaporation methods. The largest decrease in the lattice thermal conductivity owing to the scattering of long-wavelength phonons on the grain interfaces was observed in the films of solid solutions p-Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ deposited by discrete evaporation on the amorphous substrates of polyimide without thermal treatment. It is shown that in the p-Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ films with low thermal conductivity the energy dependence of the relaxation time is enhanced, which is specific for the topological insulators. The electronic thermal conductivity was determined taking into account the effective scattering parameter in the relaxation time approximation versus energy in the Lorentz number calculations. The observed increase of the electronic thermal conductivity within the temperature range of 40 - 80 K is related to the weakening of the electrical conductivity temperature dependence and is determined by the increase in the effective scattering parameter at low temperatures due to the effect of scattering on the point antisite and impurity defects. A correlation was established between the thermal conductivity and features of the morphology of the interlayer surface (0001) in the studied films.