Enhancement of the Seebeck coefficient and power factor in gated silicene superlattices induced by aperiodicity

Abstract

This paper theoretically investigates the impact of aperiodic sequences in the ballistic transport and thermoelectric effect in silicene gated superlattices. In our analysis, we have implemented the well-known Fibonacci, Thue–Morse, and triadic Cantor type sequences. The transfer matrix technique and the Landauer–Bütikker formalism are used to calculate the transmission probability and the conductance, respectively. The Cutler–Mott formula is employed to estimate the Seebeck coefficient, and the thermoelectric power factor is then obtained. We found that the transmission minibands of aperiodic superlattices exhibit a much more fragmented structure in comparison to that reported in the periodic case. Consequently, the conductance curve presents a more pronounced oscillating shape, which improves the thermoelectric properties. In particular, the Seebeck coefficient has reached values up to 78.2 mV/K for Fibonacci, 233.0 mV/K for Thue–Morse, and 436.3 mV/K for Cantor. In addition, the power factor has been substantially increased, reaching peaks of approximately 8.2, 50.2, and 2.1 nW/K2 for the mentioned sequences, respectively. The best results were obtained for spindown (spinup) charge carriers in the K (K′) valley. Besides, an additional improvement is obtained by considering superior generations of the aperiodic sequences. Finally, our findings are supported through the redistribution of the density of the states, which is induced by the aperiodicity of the nanostructure as well as by the low-dimensionality of the thermoelectric device.

Carbon Nanotubes for Active Refrigeration and Cooling in Micro and Mesoscale Systems

“…Commonly used methods include the Boltzmann equation, [84][85][86][87] the Rode's method, [88][89][90][91][92][93] and the quantum transmission matrices. [94][95][96][97][98] The active thermal conductivity is different than and imposed upon the passive thermal conductivity of κ that is contributed by both lattice and charge carriers. Zebarjadi et al [51] have pointed out that though the energy efficiency of a thermoelectricity generator prefers an enhanced figure of merit, the solid-state thermoelectric refrigeration and cooling also prefers thermoelectric materials with large values of both thermal conductivity and/or power factor.…”

Enhanced electron transport and self-similarity in quasiperiodic borophene nanoribbons with line defects

“…Note that although the electron transport in both quasiperiodic graphene and silicene superlattices has been widely investigated, [57][58][59][60][61][62] the width effect is neglected because all these superlattices are described by the massless Dirac Hamiltonian. In contrast, the quasiperiodic BNRs are described by the tight-binding Hamiltonian in eqn (1), which allows us to consider the width effect.…”

“…This is different from the previous Fibonacci model where all the electronic states are critical. 40,[49][50][51][52][53][54][55][56][57][58][59][60][61][62] (ii) The {1, 21} BNR will present excellent conducting ability for N = 5 and 20 because of the blank area around the Fermi level E F = 0 [Fig. 2(a) and (c)].…”

“…Therefore, we conclude that the energy spectra of the quasiperiodic BNRs are multifractal, complementing previous quasiperiodic models whose potential energies are generated following, e.g., the Fibonacci sequence. [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] In particular, both delocalized and critical electronic states exist in the quasiperiodic BNRs, in contrast to the Fibonacci model and quasiperiodic graphene superlattices which only possess critical states. [49][50][51][52][53][54][55][56][57][58][59][60][61][62] B. Self-similarity of quasiperiodic BNRs Finally, we investigate whether the important characteristic of self-similarity still holds in the quasiperiodic BNRs.…”

“…51,52 Besides, the Fibonacci model has also been studied theoretically in other systems, such as quantum dots 53 and double-stranded DNA. [54][55][56] In particular, both quasiperiodic graphene and silicene superlattices have been constructed by manipulating external gate voltages and their electron transport properties have been investigated theoretically, [57][58][59][60][61][62] finding that the graphene superlattices possess a Cantor-like energy spectrum with tunable bandgaps. [57][58][59] Note that all these quasiperiodic systems are implemented by modulating the potential energies according to quasiperiodic sequences, e.g.…”