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In this work, we study systematically low-energy bands, optical absorbance and spin/valley-Hall conductivity of silicene and germanene in the presence of a perpendicular electric field. Our analytical calculations indicate that both silicene and germanene are semiconductors with a tiny energy gap and we can control their energy gap by the perpendicular electric field. Our calculations also demonstrate that the low-frequency optical absorbance of silicene is much greater than that of germanene and the external electric field plays an important role in determining the optical absorption peaks. When the Fermi level is in the forbidden band, the Hall conductivity is quantized, while spin/valley-Hall conductivities of both silicene and germanene depend strongly on the Fermi energy when the Fermi level is in the conduction band. Analytical results for spin/valley-Hall conductivities of silicene and germanene are presented in detail in this work. [ABSTRACT FROM AUTHOR]

In the present work, we consider systematically the electronic and optical properties of two-dimensional monolayer germanium monosulfide (GeS) under uniaxial strains along armchair (AC-strain) and zigzag (ZZ-strain) directions. Our calculations show that, at the equilibrium state, the monolayer GeS is a semiconductor with an indirect band gap of 1.82 eV. While monolayer GeS is still an indirect band gap semiconductor under ZZ-strain, an indirect–direct energy gap transition can be found in the monolayer GeS when the AC-strain is applied. The optical spectra of the monolayer GeS have strong anisotropy in the investigated energy range from 0 eV to 8 eV. Based on optical properties, we believe that the monolayer GeS is a potential candidate for applications in energy conversion and optoelectronic technologies. [ABSTRACT FROM AUTHOR]

Using density functional theory, we have studied the structural, electronic and optical properties of two-dimensional graphene-like C2N nanosheet under in-plane strains. Our results indicate that the C2N nanosheet is a semiconductor with a direct band gap of 1.70 eV at the equilibrium state opening between the highest valence band and lowest conduction band located at the Γ point. The band gap of the C2N nanosheet decreases with the increasing of both uniaxial/biaxial strains. In the presence of the strain, we found band shift and band splitting of the occupied and unoccupied energy states of the valence and conduction bands, resulting in a decrease of the band gap. Furthermore, the absorption and reflectance spectra for the C2N nanosheet have a broad peak around 2.6 eV, where a maximum absorption value is up to 3.2×10-5cm-1 and reflectance is about 0.27%. Moreover, our calculations also show that the optical properties of the C2N nanosheets can be controlled by applying the biaxial and uniaxial strains. The obtained results might provide potential applications for the C2N nanosheets in nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

We theoretically address the electronic structure of mono- and simple bi-layer armchair graphene nanoribbons (AGNRs) when they are infected by extrinsic charged dilute impurity. This is done with the aid of the modified tight-binding method considering the edge effects and the Green's function approach. Also, the interplay of host and guest electrons are studied within the full self-consistent Born approximation. Given that the main basic electronic features can be captured from the electronic density of states (DOS), we focus on the perturbed DOS of lattices corresponding to the different widths. The modified model says that there is no metallic phase due to the edge states. We found that the impurity effects lead to the emergence of midgap states in DOS of both systems so that a semiconductor-to-semimetal phase transition occurs at strong enough impurity concentrations and/or impurity scattering potentials. The intensity of semiconductor-to-semimetal phase transition in monolayer (bilayer) ultra-narrow (realistic) ribbons is sharper than bilayers (monolayers). In both lattices, electron-hole symmetry breaks down as a result of induced-impurity states. The findings of this research would provide a base for future experimental studies and improve the applications of AGNRs in logic semiconductor devices in industry. [ABSTRACT FROM AUTHOR]

Hot electrons cooling by phonons in GaAs/AlAs cylindrical quantum wire (CQW), under the influence of an intense electromagnetic wave (EMW), is studied theoretically. Analytic expression for the electron cooling power (CP) is derived from the quantum transport equation for phonons, using the Hamiltonian of interacting electron-optical phonon system. Both photon absorption and emission processes are considered. Numerical results show that the CP reaches maximum when the energy difference between electronic subbands equals the energy of an optical phonon plus the photon energy. Under the influence of the EMW, the negative CP is observed showing that electrons gain energy from phonon and photon instead of losing their energy. Also, the CP increases with increasing the EMW amplitude. Our results theoretically clarify the mechanism of the electron cooling process by phonons in the GaAs/AlAs CQW under the EMW, which is of significance for designing and fabricating high-speed nanoelectronic devices based on this material. [ABSTRACT FROM AUTHOR]

In this work, the phonon-assisted cyclotron resonance in a special symmetric quantum well is studied in detail by evaluating the magneto-optical absorption coefficient (MOAC) and the full width at half maximum (FWHM). The results include the two-photon absorption process and the electron-phonon interaction as well. The influence of the magnetic field, the quantum well parameter, and the temperature on the MOAC and the FWHM is illustrated plainly. Our results are in good agreement with those accessible to the theoretical and experimental works of literature. In addition, we found a new rule of the temperature-dependent FWHM for the phonon absorption process, which should be examined by an experiment work in the future. [ABSTRACT FROM AUTHOR]