Quantum and classical thermoelectric transport in quantum dot nanocomposites

Abstract

Spontaneous emission control of single quantum dots by electromechanical tuning of a photonic crystal cavity Appl. Phys. Lett. 101, 091106 (2012) Energy states and carrier transport processes in metamorphic InAs quantum dots J. Appl. Phys. 112, 034309 (2012) High-frequency gate manipulation of a bilayer graphene quantum dot Appl. Phys. Lett. 101, 043107 (2012) Magnetovoltaic effect in a quantum dot undergoing Jahn-Teller transition Appl. Phys. Lett. 101, 023120 (2012) Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime Quantum dot nanocomposites are potentially high-efficiency thermoelectric materials, which could outperform superlattices and random nanocomposites in terms of manufacturing cost-effectiveness and material properties because of the reduction of thermal conductivity due to the phononinterface scattering, the enhancement of Seebeck coefficient due to the formation of minibands, and the enhancement of electrical conductivity due to the phonon-bottleneck effect in electronphonon scattering for quantum-confined electrons. In this paper, we investigate the thermoelectric transport properties of quantum dot nanocomposites through a two-channel transport model that includes the transport of quantum-confined electrons through the hopping mechanism and the semiclassical transport of bulk-like electrons. For the quantum-confined electrons whose wave functions are confined in the quantum dots with overlapping tail extending to the matrix, we develop a tightbinding model together with the Kubo formula and the Green's function method to describe the transport processes of these electrons. The formation of minibands due to the quantum confinement and the phonon-bottleneck effect on carrier-phonon scattering are considered. For transport of bulk-like electrons, a Boltzmann-transport-equation-based semiclassical model is used to describe the multiband transport processes of carriers. The intrinsic carrier scatterings as well as the carrier-interface scattering of these bulk-like electrons are considered. We then apply the two-channel transport model to predict thermoelectric transport properties of n-type PbSe/PbTe quantum dot nanocomposites with PbSe quantum dots uniformly embedded in the PbTe matrix. The dependence of thermoelectric transport coefficients on the size of quantum dots, interdot distance, doping concentration, and temperature are studied in detail. Due to the formation of minibands and the phonon-bottleneck effect on carrier-phonon scattering, we show that simultaneous enhancement of electrical conductivity and Seebeck coefficient can be realized in quantum dot nanocomposites. Our study could shed some light on the design of high-efficiency thermoelectric materials for energy conversion and thermal management.

Optimal thermoelectric figure of merit in Bi2Te3/Sb2TeZhou1, Wang2, Sharp3 et al. 2012Phys. Rev. BSelf Cite

“…17 However, the relaxation time of quantum-confined carriers could be prolonged for over two orders of magnitude at the upper edge of the minibands due to the phonon bottleneck effect in carrier-phonon scattering. 29 The competition between the contributions of quantum-confined and bulk-like carriers will dictate the electrical conductivity in QD NCs.…”

“…29 We choose the height of the confinement potential to be 0.25 eV and choose the valence band offset between QDs and matrix to be 0.08 eV in our calculations. We note that it is really difficult to determine the height of the confinement potential in practice since it depends on the band offset between QDs and matrix materials, the band bending due to depletion effect near the interface, and the surface charge trapping at the interface.…”

“…The wave functions of the quantum-confined carriers are calculated by solving the Schrödinger equation with a periodic cosine-shaped confinement potential 29,35 of QD arrays.…”

Thermoelectric power factor of nanocomposite materials from two-dimensional quantum transport simulations

“…While the impact of nanoinclusions on the thermal conductivity is well documented [18,45], previous works are not as clear on their impact on the power factor, with results varying significantly, from only small influence [30,31,34,46], to large potential improvements [25,36,42,47]. Thus, it is imperative that a high level of understanding on the influence of nanoinclusions on the power factor, both qualitative and quantitative, is also established, if ZT is to be maximized.…”

“…However, the complexity of the electronic transport, combining semiclassical effects, quantum effects, ballistic and diffusive regimes, as well as the geometry details, makes accurate modeling a difficult task. Several works in the literature use semiclassical models, simplified geometries, and various approximations to provide understanding of transport in such systems [28,[46][47][48].…”