Fermi energy

About: Fermi energy is a research topic. Over the lifetime, 10458 publications have been published within this topic receiving 263630 citations.

Tunable Multi-band Switch with Uncoupled Graphene-based Metamaterial Patches

Abstract: We present the tunable multiple plasmon-induced transparency (PIT) in the terahertz region by using a metamaterial made of two graphene bands and a graphene square ring. As the different modes of multiple PIT effects are independent of each other, the physical mechanism behind multiple PIT effects can be revealed by CMT theory. The PIT window changes significantly with the Fermi energy levels and structural parameters of graphene. The both three resonant frequencies increase linearly with the parameters and the Fermi energy changing, which can exhibit high sensitivities and figure of merit (FOM). Meanwhile, the amplitude modulation system can reach 99.63%, which can achieve excellent photoelectric switching. In addition, the group index can be as high as 2739. Therefore, the graphene-based metamaterial could be widely used in switches, modulators, excellent slow-light functional devices and filters in the terahertz region.

Switchable dual-broadband to single-broadband terahertz absorber based on hybrid graphene and vanadium dioxide metamaterials

Abstract: Switchable and tunable broadband perfect absorbers have drawn great interest in a wide range of applications, including modulation, energy harvesting, and spectroscopy. Here, we propose a switchable and tunable terahertz (THz) metamaterial absorber with dual-broadband, single-broadband perfect absorption using graphene and vanadium dioxide (VO2). Simulation results show that, when VO2 is in the insulated state, this design behaves as a dual-broadband absorber with over 90% absorption in 0.73 THz–1.53 THz and 3.03 THz–3.64 THz under normal incidence. When VO2 is in the metallic state and the graphene Fermi energy is set as 0.01 eV, this design acts as a single-broadband absorber with over 90% absorption in 1.00 THz–3.55 THz and the fractional bandwidth reaches 112%, which is much larger than the previously reported values. The absorption rate can be dynamically tuned by individually changing the conductivity of VO2 and the Fermi energy of graphene. Moreover, this design exhibits polarization-insensitive and wide-incident-angle behaviors for both TE and TM waves. Such a design may have potential applications in many fields, such as thermal detectors, modulators, and stealth technology.

Antiphase boundaries in III-V semiconductors: Atomic configurations, band structures, and Fermi levels

Abstract: Here, we comprehensively investigate the atomic structures and electronic properties of different antiphase boundaries in III-V semiconductors with different orientations and stoichiometries, including {110}, {100}, {111}, {112} and {113} ones, based on first-principle calculations. Especially, we demonstrate how the ladder or zigzag chemical bond configuration can lead for the different cases to a gapped semiconducting band structure, to a gapped metallic band structure or to a non-gapped metallic band structure. Besides, we evidence that the ladder APB configurations impact more significantly the Fermi energy levels than the zigzag APB configurations. We finally discuss how these different band structures can have some consequences on the operation of monolithic III-V/Si devices for photonics or energy harvesting.

On the Generalized Distribution Functions in Heavily Doped Nano Materials at Terahertz Frequency

Abstract: In this chapter, we present a simplified analysis of the generalized distribution function of the carriers in heavily doped materials in the form $$F(\overline{E}) = [1 + A + \exp (y)]^{ - 1}$$ where $$A$$ is a constant and the other variables are defined in the text. The substitution $$A = 0$$ and $$- 1$$ lead to the well-known Fermi–Dirac statistics and Maxwell–Boltzmann distribution, respectively. The substitutions $$A = 0$$ and $$y = 0$$ together with $$A = - 4$$ and $$y = 0$$ lead to the well-known Pauli’s exclusion principle ( $$\pm (1/2)$$ ), whereas the substitutions $$A = i - 1$$ $$(i = \sqrt { - 1} )$$ and $$y = 0$$ together with $$A = - 3 - i$$ and $$y = 0$$ lead to the complex values of the Pauli’s spin in the tail zone as $$\pm (1 - i)/2$$ , respectively. Because of the complex Pauli’s spin value, the electron energy component due to the spin $$g$$ factor along the direction of the magnetic field $$B$$ in heavily doped electronic materials forming band tails in the tail zone generates the magnitude of the electron energy as 71% g times the cyclotron resonance energy together with the phase value $$\pm \,(\,\pi /4)$$ in this case. We have also shown the Bose Einstein statistics in this context. Besides, the cases of terahertz frequency, heavy doping and intense electric field can be covered by replacing the value of $$\overline{E}$$ under the mentioned conditions.

High Thermoelectric Properties in Quasi-One-Dimensional Organic Crystals

Abstract: Recently, there has been a significant attention in thermoelectric (TE) applications of organic materials due to more diverse and tunable properties and less cost in comparison to inorganic counterparts. We present a short review about TE properties of organic materials and especially of quasi-one-dimensional (Q1D) organic crystals of p-type tetrathiotetracene-iodide, TTT2I3, and of n-type tetrathiotetracene-tetracyanoquinodimethane, TTT(TCNQ)2. To describe TE properties, we apply a physical model accounting for two of the most important electron-phonon interactions. One interaction is of deformation potential type and the other is of polaron type. The scattering of charge carriers on point-like impurities and on thermally activated defects is considered as well. It is shown that due to a partial compensation of above mentioned electron-phonon interactions, energy relaxation time of charge carriers increases significantly for a narrow strip of states in conduction band, with Lorentzian-type maximum as a function of charge carrier energy. The height of the maximum is limited by supplementary internal interactions and impurity scattering processes and may be rather high in sufficiently purified crystals. Charge carriers near this maximum will possess an increased mobility. If the concentration of charge carriers is optimized so as the Fermi energy is close to the states that correspond to this maximum, it is predicted to obtain high TE properties.