We study the resonant tunneling effects through double barrier graphene systems (DBGSs). We have considered two types of DBGSs in order to take into account or rule out Klein tunneling effects: (1) the well-known and documented electrostatic-barrier structures (EBSs) created by means of electrostatic probes that act perpendicularly to the graphene sheet; and (2) substrate-barrier structures (SBSs) built sitting the graphene layer on alternating substrates, such as SiO2 and SiC, which are capable of non-open and open an energy bandgap on graphene. The transfer matrix approach is used to obtain the transmittance, linear-regime conductance, and electronic structure for different set of parameters such as electron energy, electron incident angle, barrier, and well widths. Particular attention is paid to the asymmetric characteristics of the DBGSs, as well as to the main differences between Klein and non-Klein tunneling structures. We find that: (1) the transmission properties can be modulated readily changing the energy and angle of the incident electrons, the widths of the well and barrier regions; (2) the linear-regime conductance is easily enhancing, diminishing, and shifted changing from symmetric to asymmetric DBGSs configuration overall in the case of non-Klein tunneling structures; (3) the conductance shows an oscillatory behavior as function of the well width, with peaks that are directly related to the opening and opening-closure of bound-state subbands for EBSs and SBSs, respectively. Finally, it is important to mention that electrostatic DBGSs or substrate DBGSs could be more suitable depending on a specific application, and in the case of non-Klein tunneling structures, they seem possible considering the sophistication of the current epitaxial growth techniques and whenever substrates that open an energy bandgap on graphene, without diminishing the carrier's mobility, be experimentally discovered.

Low-dimensional thermoelectricity opens the possibility of improving the performance and the efficiency of thermoelectric devices by redistributing the electron density of states through the reduction of dimensionality. In this work, we explore this possibility in silicene by reducing its dimensionality through the periodic arrangement of gated electrodes, the so-called gated silicene superlattices. Silicene electrons were described quantum relativistically. The transmission, conductance, and thermoelectric properties were obtained with the transfer matrix method, the Landauer-Büttiker formalism, and the Cutler-Mott formula, respectively. We find that the redistribution of the density of states together with the intrinsic characteristics of silicene, the local bandgap and the large spin-orbit coupling, contribute to the enhancement of the thermoelectric properties. In particular, the Seebeck coefficient and the power factor reach values of a few mV/K and nW/K2. These findings in conjunction with the low thermal conductivity of silicene indicate that silicene-based nanostructures could be the basis of more efficient thermoelectric devices.

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.

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The superposition principle is one of the cornerstones of physics. In low-dimensional systems, it is routinely used to model the potential profile. That is the case of coupled [Formula: see text]-doped quantum wells, for which, several works have studied the transport and optoelectronic properties. However, the Poisson equation determines the potential profile is not linear, and the superposition principle is not at all valid. The aim of this work is to correct some of the inconsistencies of the mentioned models for coupled [Formula: see text]-doped quantum wells. In the framework of Thomas–Fermi approximation, we calculated the potential profile, the wave functions, the energy values and the relative absorption coefficient for the double system compared to an isolated delta system in terms of impurity density and distance between [Formula: see text]-wells. We found a red shifting in the absorption coefficient when the interlayer distances increase, in addition, an enhancement in the absorption coefficient is detected for a specific separation distance. Our results agree with ab-initio calculations reported for the electronic structure.

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