Tuning the electrical and optical anisotropy of a monolayer black phosphorus magnetic superlattice

Effect of tensile deformation on the optoelectronic properties of black phosphine-doped lithium atoms

CONTEXT

First-principles calculations based on the generalized gradient approximation gradient and the Perdew-Burke-Ernzerhof function (GGA-PBE generalized function) are carried out on the intrinsic and lithium-doped black phosphine systems to investigate the effects of different uniaxial tensile deformations on the electronic and optical properties of the systems. It is shown that the structural stability of the intrinsic and lithium-doped systems decreases with increasing tensile deformation, and all systems are most stable at 0% tensile deformation. The intrinsic black phosphazene system is a direct band gap semiconductor, and its band gap increases and then decreases with tensile deformation and reaches a maximum value of 1.086 eV at 4%. Lithium doping closes the band gap of the black phosphazene system, which is metallic in nature, but the band gap is opened up when the tensile deformation is 4-6%. From the density of states analysis, the density of states of all systems is basically contributed by the s and p orbitals, with little contribution from the d orbitals, and the contribution from the p orbitals is dominant. From the analysis of optical properties, the increase of tensile deformation causes the absorption peaks of the intrinsic system to redshift then blueshift then redshift, causes the absorption peaks of the lithium-doped system to redshift, and causes the reflection peaks of all systems to redshift. In addition, lithium doping blueshifts the absorption and reflection peaks of the systems compared to the intrinsic black phosphazene system.

METHODS

Using the CASTEP section of the Materials Studio software, first-principle calculations based on density functional theory are done on the top-site doped lithium atoms of monolayer black phosphine under uniaxial stretching deformation in the a-direction, and the generalized gradient approximation gradients and Perdew-Burke-Ernzerhof functions (GGA-PBE generalized functionals) are used for the optimization and approximation process. The optimization parameters are set for the supercell structure: its plane-wave truncation energy is set to 400 eV, its Brillouin zone K-point grid is set to 3*3*3, its self-consistent field iteration accuracy convergence value is 2.0e-6 eV/atom, the convergence basis of its structural optimization is 0.02 eV/ Å, and the convergence of the stress value is 0.05 gpa. During the optimization period, the interaction force between atoms is 0.03 eV/ Å and the atomic displacement is less than 0.001 Å. To eliminate the effect of interlayer forces, a vacuum layer with a thickness of 15 Å is placed in its vertical direction (i.e., c-axis direction).

Tuning the magnetoresistance properties of phosphorene with periodic magnetic modulation

Periodic superlattices constitute ideal structures to modulate the transport properties of two-dimensional materials. In this paper, we show that the tunneling magnetoresistance (TMR) in phosphorene can be tuned effectively through periodic magnetic modulation. Deltaic magnetic barriers are arranged periodically along the phosphorene armchair direction in parallel (PM) and anti-parallel magnetization (AM) fashion. The theoretical treatment is based on a low-energy effective Hamiltonian, the transfer matrix method and the Landauer-Büttiker formalism. We find that the periodic modulation gives rise to oscillating transport characteristics for both PM and AM configurations. More importantly, by adjusting the electrostatic potential appropriately we find Fermi energy regions for which the AM conductance is reduced significantly while the PM conductance keeps considerable values, resulting in an effective TMR that increases with the magnetic field strength. These findings could be useful in the design of magnetoresistive devices based on magnetic phosphorene superlattices.

Electronic structure and optical properties of B-, N-, and BN-doped black phosphorene using the first-principles

The structural stability, electronic structure, and optical properties of BN-doped black phosphorene systems at different concentrations were investigated using a density generalized theory approach based on the first principles. BN-doped black phosphorene was found to be more stable than B and N atom doping. With the increase of doping concentration, the stability of the structure gradually decreases, and the structure of the system with 25% doping concentration is the most stable. The intrinsic and N-doped black phosphorenes are direct bandgap semiconductors, and B and BN doping make the black phosphorene change from direct bandgap to the indirect bandgap. The total density of states is mainly contributed by the p-state electrons of the B and P atoms, and the N atoms have a role in the local density of states with little contribution to the overall one. The black phosphorene undergoes charge transfer between the B and N atoms. The amount of charge transfer increases with the increase of doping concentration. The BN-doped black phosphorene system is blue-shifted at the absorption and reflection peaks compared to the intrinsic black phosphorene system. From the dielectric constant, it is found that the doped system is shifted towards higher energy at the highest peak, leading to an increase in the intensity of the electric field generated by light, which is beneficial to increase the efficiency of photovoltaic power generation. The photoconductivity decreases and shifts toward higher energy after doping, with the most pronounced performance at BN doping concentrations of 12.5% and 25%.

Single pixel wide gamut dynamic color modulation based on a graphene micromechanical system

Dynamic color modulation in the composite structure of a graphene microelectromechanical system (MEMS)-photonic crystal microcavity is investigated in this work. The designed photonic crystal microcavity has three resonant standing wave modes corresponding to the three primary colors of red (R), green (G) and blue (B), forming strong localization of light in three modes at different positions of the microcavity. Once graphene is added, it can govern the transmittance of three modes. When graphene is located in the antinode of the standing wave, it has strong light absorption and therefore the structure's transmittance is lower, and when graphene is located in the node of the standing wave, it has weak light absorption and therefore the structure's transmittance is higher. Therefore, the graphene absorption of different colors of light can be regulated dynamically by applying voltages to tune the equilibrium position of the graphene MEMS in the microcavity, consequently realizing the output of vivid monochromatic light or multiple mixed colors of light within a single pixel, thus greatly improving the resolution. Our work provides a route to dynamic color modulation with graphene and provides guidance for the design and manufacture of high resolution, fast modulation and wide color gamut interferometric modulator displays.

Quenching effect of oscillating potential on anisotropic resonant transmission through a phosphorene electrostatic barrier

The anisotropy in resonant tunneling transport through an electrostatic barrier in monolayer black phosphorus either in presence or in absence of an oscillating potential is studied. Non-perturbative Floquet theory is applied to solve the time dependent problem and the results obtained are discussed thoroughly. The resonance spectra in field free transmission are Lorentzian in nature although the width of the resonance for the barrier along the zigzag (Г–Y) direction is too thinner than that for the armchair (Г–X) one. Resonant transmission is suppressed for both the cases by the application of oscillating potential that produces small oscillations in the transmission around the resonant energy particularly at low frequency range. Sharp asymmetric Fano resonances are noted in the transmission spectrum along the armchair direction while a distinct line shape resonance is noted for the zigzag direction at higher frequency of the oscillating potential. Even after the angular average, the conductance along the Г–X direction retains the characteristic Fano features that could be observed experimentally. The present results are supposed to suggest that the phosphorene electrostatic barrier could be used successfully as switching devices and nano detectors.

Rashba spin-orbit coupling enhanced two-photon absorption and its polarization dependence in monolayer black phosphorus

We investigate theoretically the impact of Rashba spin-orbit coupling (RSOC) effect to two-photon absorption (TPA) and its dependence on the polarization direction of the incident light in monolayer black phosphorus (BP) starting from an anisotropic two band k·p model. It is found that the TPA is enhanced several times by RSOC effect which is tuned by the external electric field. And the TPA response shows highly anisotropic, changing periodically with the polarization direction of incident linearly polarized light as the function of cos⁴θ approximatively. The TPA coefficient reaches its maximum when the polarization direction is aligned along the armchair direction (x-direction), while falls into its minimum along the zigzag direction (y-direction).