Low-temperature enhancement of the thermoelectric Seebeck coefficient in gated 2D semiconductor nanomembranes
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An increasing need for effective thermal sensors, together with dwindling energy resources, have created renewed interests in thermoelectric (TE), or solid-state, energy conversion and refrigeration using semiconductor based nanostructures. Effective control of electron and phonon transport due to confinement, interface, and quantum effects has made nanostructures a good way to achieve more efficient thermoelectric energy conversion. Theoretically, a narrow delta-function shaped transport distribution function (TDF) is believed to provide the highest Seebeck coefficient, but has proven difficult to achieve in practice. We propose a novel approach to achieving a narrow window-shaped TDF through a combination of a step-like 2-dimensional density-of-states (DOS) and inelastic optical phonon scattering. A shift in the onset of scattering with respect to the step-like DOS creates a TDF which peaks over a narrow band of energies. We perform a numerical simulation of carrier transport in silicon nanoribbons based on numerically solving the coupled Schrödinger-Poisson equations together with transport in the semi-classical Boltzmann formalism. Our calculations confirm that inelastic scattering of electrons, combined with the step-like DOS in 2-dimensional nanostructures leads to the formation of a narrow window-function shaped TDF and results in enhancement of Seebeck coefficient beyond what was already achieved through confinement alone. A further analysis on maximizing this enhancement by tuning the material properties is also presented.
KeywordsThermo-electric Seebeck Phonon Schroedinger–Poisson Boltzmann transport
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