343 research outputs found

    Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides

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    The electronic and thermoelectric properties of one to four monolayers of MoS2_{2}, MoSe2_{2}, WS2_{2}, and WSe2_{2} are calculated. For few layer thicknesses,the near degeneracies of the conduction band KK and Σ\Sigma valleys and the valence band Γ\Gamma and KK valleys enhance the n-type and p-type thermoelectric performance. The interlayer hybridization and energy level splitting determine how the number of modes within kBTk_BT of a valley minimum changes with layer thickness. In all cases, the maximum ZT coincides with the greatest near-degeneracy within kBTk_BT of the band edge that results in the sharpest turn-on of the density of modes. The thickness at which this maximum occurs is, in general, not a monolayer. The transition from few layers to bulk is discussed. Effective masses, energy gaps, power-factors, and ZT values are tabulated for all materials and layer thicknesses

    One Dimensional Quantum Transport: Characterization and Device Applications

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    With the maturing of the technologies of molecular beam epitaxy and electron beam direct write, semiconductor crystals can be engineered on the size scale of a de Broglie wavelength in both the vertical and lateral directions. On this scale, the wave nature of the electrons becomes manifest and it becomes possible to conceive of devices that exploit wave properties such as resonance and diffraction. In this work, a complete fabrication process for building sub-micron conducting channels analogous to a waveguide in a high mobility GaAs - AlGaAs heterostructure is developed. The waveguides are characterized with respect to the number of transverse modes and the phase coherence length. A novel device structure analogous to a microwave resonator is fabricated and tested and found to give results in good agreement with theor

    Thermoelectric properties of Bi2Te3 atomic quintuple thin films

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    Motivated by recent experimental realizations of quintuple atomic layer films of Bi2Te3,the thermoelectric figure of merit, ZT, of the quintuple layer is calculated and found to increase by a factor of 10 (ZT = 7.2) compared to that of the bulk at room temperature. The large enhancement in ZT results from the change in the distribution of the valence band density of modes brought about by the quantum confinement in the thin film. The theoretical model uses ab initio electronic structure calculations (VASP) with full quantum-mechanical structure relaxation combined with a Landauer formalism for the linear-response transport coefficients.Comment: 4 figures, submitted to AP