Enhanced thermopower and energy filtering effect from synergetic scattering at heterojunction potentials in the thermoelectric composites with semiconducting nanoinclusions

Abstract

In nanocomposites consisting of a semiconductor matrix embedded with different kinds of semiconductors, two types of heterojunctions are configured theoretically. The potential energies for electrons in the heterojunctions are derived by using the Thomas–Fermi approximation and depletion layer approximation. Assuming occurrence of synergetic scattering of ionized impurities and heterojunction potentials, and by using the defined formula we have proposed previously [45], the effective relaxation time (τeff) was calculated in a wide energy ranges for four radii of spheres (r0=10–40nm) and four electron concentrations (n=(0.05–0.5)×1020cm−3). Then the scattering parameters (λ) at different temperatures (T=100–850K) are obtained by fitting the calculated data to formula τeff=τ0Eλ−1/2. The results indicate that λ depends on T, r0 and n intricately, and much stronger dependences of λ on n were observed in the composites with larger inclusions (r0=30nm and 40nm). In the ranges of T, r0 and n investigated here, all the values of λ exceed 3.9, and the largest reaches 4.59. Seebeck coefficients calculated using the λ values for synergetic scattering are enhanced considerably as compared to those for the single scattering. The present results demonstrate that heterojunction potentials in semiconductor-based nanocomposites with semiconducting inclusions can give rise to enhanced energy filtering effect if synergetic scattering prevails, thereby elevating thermopower and thermoelectric performance of the nanocomposite systems.