Monolayer Black Phosphorus Research Articles

The effects of electric field and strain on the BP/GeTe van der Waals heterojunction

Recently, van der Waals heterojunctions (vdWHs) constructed from two two-dimensional materials have attracted considerable attention. In particular, vdWHs based on black phosphorus (BP) have shown excellent photoelectric properties. In this work, we construct a BP/GeTe vdWH and investigate its electronic and optical properties. We find that the BP/GeTe vdWH has a type-II band alignment. Its optical absorption exhibits a red shift compared to the freestanding BP and GeTe monolayers. The electric field and strain effects on the BP/GeTe vdWH are also investigated. The band offsets can be modulated by the electric field and the strain. The BP/GeTe vdWH will convert from type-II to type-I when applying an electric field and to type-III under strain, which will expand the application of BP/GeTe vdWHs in transistor devices. Furthermore, the strain can significantly enhance the optical absorption and induce the red shift of the absorption edge, which indicates the broad applications of the BP/GeTe vdWH in photodetector devices.

Interfacial Interaction of Monolayer Black Phosphorus/g‐C3N4 Van Der Waals Heterojunction for Efficient Photocatalytic Hydrogen Evolution

The 2D/2D van der Waals heterojunctions have promising photocatalytic applications. However, their interfacial interaction and photocatalytic mechanism are still unclear. Herein, monolayer black phosphorus (BP)/graphitic carbon nitride (GCN) heterojunction photocatalytic hydrogen evolution is systematically investigated using the density‐functional theory method. It is indicated in the results that BP/GCN heterojunction structure distortion and interface interaction change its electronic structure and photocatalytic performance. The hydrogen‐adsorption free energy of BP/GCN heterojunction is −0.28 eV, indicating that the BP/GCN heterojunction has a high catalytic activity for hydrogen production. Calculated Bader charge and Fermi energy level show that a built‐in electric field from BP to GCN forms in its interface. The energy barrier and built‐in electric field promote the recombination of photogenerated electrons in GCN conduction band and photogenerated holes in BP valence band; electrons on the BP conduction band and holes on the GCN valence band are effectively separated in space; and more electrons and holes can participate in redox reactions on the surface. The BP/GCN heterojunction is a type Z heterojunction. Significant improvement in photocatalytic reaction efficiency is attributed to the type Z photocatalytic mechanism and small free energy of hydrogen adsorption. Herein, it is aimed to offer insights into the photocatalytic mechanism of 2D/2D heterojunctions.

Near-unity broadband infrared absorption in a graphene-black phosphorus bimodal triple-layer structure

It is well known that both graphene and monolayer black phosphorus (BP) can excite and generate surface plasmonic resonances in the infrared spectrum, providing suitable conditions for strong light-matter interactions. To take full advantage of this benefit, a three-layered infrared absorbing structure with broadband absorption effect based on a hybrid graphene-BP metamaterial was developed. Using numerical research methods, the absorption effect of the structure could be well modulated by adjusting the geometrical parameters of the structure and the doping levels of graphene and BP. In addition, the sensitivity of the structure to the angle of incidence is also investigated. By optimizing the previous parameters, the structure achieves an absorption of more than 87.5% in the wavelength range from 10.1 to 24.5 um and a maximum absorption of 99.97%. The proposed broadband infrared structure could have many potential applications in infrared sensing, bio-imaging and environmental monitoring.

Curvature-induced phase transitions in two-dimensional polymorphic materials

Many two-dimensional (2D) materials are polymorphic and can exhibit multiple lattice structures with similar stability although the chemical compositions are fixed. However, controlled synthesis of these 2D materials with a desirable lattice structure remains a daunting task. Here, we employ the outstanding structural bendability of 2D materials enabled by their atomic thickness and propose a strategy to achieve a phase control by introducing curvature in the materials. This idea is built on the lattice-dependent bending stiffness of 2D materials which can lift the energy degeneracy of polymorphic phases upon bending deformation. We apply our idea to the switching of stability between black and blue phosphorus monolayers as well as between semiconducting and metallic MoTe2 monolayers, which are supported by first-principles calculations including vibrational energy corrections. The black phosphorus can be transformed into blue phosphorus at a curvature of over 0.062 Å −1 and room temperature. Moreover, the curvature-induced phase engineering can even lead to new lattice structures, as exemplified by the emergence of hexagonal buckled SnO monolayer at small curvatures.

Theoretical Study of Intercalation Effects: Graphene and hBN Layers in Metal and Monolayer Black Phosphorus Contacts

Theoretical Study of Intercalation Effects: Graphene and hBN Layers in Metal and Monolayer Black Phosphorus Contacts

Effects of hexagonal boron nitride encapsulation on the electronic properties of Cu, Li, and O-doped black phosphorus monolayer

In this work, the structural and electronic properties of Cu, Li, and O-doped phosphorene/hexagonal boron nitride systems were studied based on density functional theory calculations. The intrinsic physical properties of the pristine phosphorene layer do not change with the addition of hexagonal boron nitride layers. While doping of phosphorene leads to strong binding energy at the interface, hence, improving the stability of the doped phosphorene/hexagonal boron nitride layers in systems. The electronic properties of the encapsulated systems change after doping. The band gap also decreases from 1.1200 eV in pristine encapsulated phosphorene to 0.3087, 0.0076, and 0.3100 eV in encapsulated phosphorene doped with Li, Cu, and O, respectively. The partial density of states and band structure diagrams show that the electronic properties of these systems shift from semiconductor to metallic behavior which can be exploited in electronic and optical applications.

Near-Field Radiative Heat Transfer between $\\beta-$GeSe monolayers: An ab initio study

ABSTRACT We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions.

Strain-Modulated Electronic and Thermal Transport of Monolayer Black Arsenic Phosphorus

In this paper, the first-principles density functional theory and non-equilibrium Green’s function method were used to investigate the effect of strain on the electronic and thermal transport of monolayer black arsenic phosphorus (B-AsP). Through this research, we found that the band gap of the monolayer B-AsP decreased under compressive strain, the electronic transport was revealed by I-V curves, and there was current at a very small voltage. The compressive strain can enhance the electronic transport, but it does not have a favorable effect on the thermal transport. When increasing the temperature at the same time for the tensile strain, the thermal transport has been improved, reflected by the ZT coefficient, which is increased by 7.76% compared with the original system. At the same time, we also used temperature to regulate the ZT coefficient. At a high temperature of 400 K, the ZT coefficient is larger than the one at room temperature by 26.11%.

Monolayer black phosphorus: Tunable band gap and optical properties

Black phosphorus, with its tunable optical band gap, has gained significant interest due to its potential applications in optoelectronics. In this study, a first-principles approach based on density functional theory is used to examine the effects of Sc, Mn, and Ni doping on the electronic structure and optical properties of black phosphorus. The results indicate that the addition of impurity atoms with varying radii leads to a shift in the position of atoms surrounding the doping site. The band gaps of the doped systems are all reduced, with the most significant reduction observed in the Ni-doped system. Compared to intrinsic black phosphorus, the doped systems exhibit higher values of the imaginary part of dielectric function, optical absorbance, refractive index, and extinction coefficient in the visible and infrared regions. These findings suggest that Sc, Mn, and Ni-doped black phosphorus are suitable for optoelectronic devices, offering improved performance in the visible and infrared spectrum.

Strain‐Induced Ferroelectric Phase Transition in Group‐V Monolayer Black Phosphorus

AbstractRecently, a variety of elemental ferroelectric materials have been predicted in group‐V monolayers. However, black phosphorus, as a well‐known group‐V system with the similar structure, seems to be absent of spontaneous ferroelectric polarization. Based on first‐principles calculations, ferroelectric phase in monolayer black phosphorus (BP) is successfully obtained by strain engineering and the driving force can be attributed to Jahn–Teller effect. In addition, the bandgap of the monolayer BP is found to be tunable with applied strain, which can be adjusted to even achieve the metal polarization states. The work not only provides a new route to explore elemental ferroelectricity in 2D materials, but also suggests strain engineering as a powerful tool in related research.

Electro- and magneto- optical properties of edge states in bilayer black phosphorene quantum dots

We theoretically investigate the electronic and optical properties of stacked bilayer black phosphorus (BBPs) quantum dots (QDs) with three typical BBPs configurations and two AB-stacking with different edge structures, using the tight-binding (TB) method. Our calculation results show that the energy levels can be affected by the different stacking configurations of BBPs. Unlike the monolayer black phosphorus (MBP), the strong inter-layer coupling in AC-stacked BBP and unsymmetrical distribution in AB-stacked BBP will enhance the optical transitions and realize a dark-to-bright transition in the electro and magneto-optical absorption spectra. The coupling strength of the edge states of different configurations is different, resulting in the difference of the properties of the three stacking configurations, which provides a feasible idea for modulating the electronic and optical properties of BBPs.

Epitaxial growth of black phosphorene monolayer on ZnO(110) substrate

As a new generation of semiconductor materials, two-dimensional black phosphorene (BlackP) has broad application prospects because of its tunable band gap and high carrier mobility. However, BlackP cannot be directly prepared on a large scale at present, which limits its further research and application. Molecular beam epitaxy is a widely used way to grow single crystal films with higher epitaxial quality, which is promising for preparing BlackP. Herein, four potential substrates ZnO(110), GaN(110), BP(110) and SiC(110) were screened, and the growth of BlackP on these substrates was studied based on first principles. Our study shows that the structure of black phosphorus monolayer on ZnO(110) is stable and P diffusion on this surface has desirable properties for BlackP growth. This study provides useful guidances for the effective preparation of BlackP and the growth of other two-dimensional materials.

Band Alignment in Black Phosphorus/Transition Metal Dichalcogenide Heterolayers: Impact of Charge Redistribution, Electric Field, Strain, and Layer Engineering

The objective of this work is to study the effects of charge redistribution, applied layer-normal electric fields, applied strain, and layer engineering on the band alignment of Black Phosphorus (BP)/Molybdenum disulphide (MoS2) heterostructure through Density Functional Theory (DFT) simulations. Black phosphorus works as a p-type material with high mobility, mechanical flexibility, and sensitivity to number of layers. Combining it with the more electronegative material, MoS2 results in strong carrier confinement and a Type II heterostructure. Charge redistribution among the layers shifts the band alignment expected from the Electron Affinity Rule. Applied external fields, strain and multiple BP layers provide band-alignment tunability within the Type II range and/or, transition to Type I and Type III heterostructures. The tunability in BP/MoS2 heterostructure may be useful as tunnel field effect transistors, rectifier diodes with tunable barrier height, reconfigurable FETs, and electro-optical modulators. Furthermore, considering heterostructures of monolayer BP with other monolayer Transitional Metal Dichalcogenides (TMD) suggests the ability to achieve different band alignment types. In our simulations, a Type I alignment is found with Tungsten diselenide (WSe2), Molybdenum diselenide (MoSe2), and Tungsten disulphide (WS2), and a Type III for Hafnium disulphide (HfS2) and Hafnium diselenide (HfSe2).

Anisotropy of the Optical Properties of Pentacene:Black Phosphorus Interfaces

Black phosphorus (BP) is a layered material with anisotropic properties. We study interfaces formed by a pentacene monolayer adsorbed on monolayer BP, a prototypical system for BP surface passivation. We place the pentacene monolayer along the zigzag and armchair directions of the BP substrate, respectively, to examine the anisotropy of the heterogeneous interfaces. We perform first-principles $GW$ plus Bethe-Salpeter equation ($GW$-BSE) calculations to determine the quasiparticle and optical properties. To quantitatively analyze the anisotropy of the optical properties, we develop a general computational scheme to decompose the interface excitons into different contributions. We find a distinct charge-transfer exciton formed when the monolayer pentacene is placed along the armchair direction, and discuss how the anisotropy of each component is modulated by the interface. Our results shine a light on the understanding of the BP surface passivation via molecular adsorption and provide a benchmark for future experimental and computational studies.

Enhanced near-field thermal radiation between black phosphorus with high electron density by BP/hBN heterostructures

ABSTRACT The black phosphorus (BP)/hexagonal boron nitride (hBN) Van der Waals heterostructure has great potential application in BP-based devices due to its higher stability than monolayer BP film. The near-field thermal radiation (NFTR) between two identical BP/hBN heterostructures with high electron density is studied to promote the application of BP-based devices. The BP/hBN heterostructures show a higher heat transfer coefficient (HTC) at a 10 nm gap distance compared to BP films with electron density n larger than 1 × 1013 cm−2, due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). Especially at n ≥ 3 × 1013 cm−2, the improvement is more than 100%. The SPPs and the HPPs couple into surface plasmon-phonon polaritons (SPPPs) out of the hyperbolic region and hyperbolic plasmon-phonon polaritons (HPPPs) inside. The SPPPs can achieve photon tunneling in the broader wavevector region than SPPs, making most of the contribution to heat transfer. The influences of the thickness of the hBN sheet and gap distance are also discussed. This scheme only effectively enhances NFTR for BP with high electron density at small nanogaps. After structural optimization, h = 2 nm is the optimal thickness for BP/hBN configuration with low electron density, such as n = 1 × 1013 cm−2. In contrast, large thickness h = 500 nm is optimal for BP with high electron density. At high electron density, a thick hBN sheet is prominent in enhancing the SPPPs in the frequencies below the type-I region and the HPPPs inside the type-II region. We further propose BP/hBN/BP heterostructures and find that HTC is further enhanced by 4.4% ~ 30.8% due to the more robust surface modes. Our work may contribute to developing BP-based near-field thermal devices and promote understanding the NFTR mechanism of BP/hBN heterostructure.

Tuning the Nonradiative Electron-Hole Recombination with Defects in Monolayer Black Phosphorus.

We use nonadiabatic (NA) molecular dynamics to demonstrate that the nonradiative electron-hole recombination is delayed and accelerated by the Stone-Wales (SWs) and phosphorus divacancy (DV-(5|7)) defects in monolayer black phosphorus (BP). Both types of defects increase the bandgap by 0.1 eV without creating midgap states. Driven by P-P stretching vibrations, the recombination proceeds within 1 ns in the SW and within 100 ps in the DV-(5|7), respectively, which occurs within 332 ps in BP. The SW defect slows down recombination because the notably reduced NA coupling combined with a large bandgap competes to the long-lived coherence. In contrast, the DV defect accelerates recombination since long-lived coherence is superior to the slightly decreased NA coupling correlated with a tiny increased bandgap. The diverse time scales rationalize the broad range of charge carrier lifetimes reported experimentally. The study provides a strategy to engineer excited-state dynamics for improving the BP-based optoelectronics.

Demonstration of giant anisotropic magnetoresistance, high spin filtering efficiency, and negative differential resistance in nanodevices based on oxygen doped black arsenic phosphorus nanoribbons

We investigate the electrical properties of pure black arsenic phosphorus and oxygen atom doped monolayer black arsenic phosphorus using first principle calculations. The density of states results reveals that oxygen atom doped black arsenic phosphorus is a magnetic semiconductor. The current-voltage characteristic curves of oxygen atom doped monolayer black arsenic phosphorus nanoribbons based devices have been determined using the non-equilibrium Green's function associated with the density function theory. The results demonstrate that the device made of doped black arsenic phosphorus has a substantial current difference between armchair and zigzag black arsenic phosphorus nanoribbons, implying that the device made of nanoribbons has a large anisotropic magnetoresistance. The spin filtering efficiency is nearly 100% at some bias voltage levels, and the transmission spectrums of the associated bias voltage window can explain the significant negative differential resistance. Furthermore, these findings suggest that oxygen atom doped black arsenic-phosphorus nanoribbons are suitable for spintronic devices.

Anisotropic exciton states and excitonic absorption spectra in a freestanding monolayer black phosphorus

The anisotropic exciton states and excitonic absorption spectra in a freestanding monolayer black phosphorus (BP) are theoretically investigated by a variationally optimized diagonalization method based on a two-dimensional (2D) nonorthogonal Laguerre basis. The exciton Hamiltonian works in the anisotropic form of the kinetic term, which has an advantage of a fully analytical expression for the matrix elements of the Hamiltonian. The energy of 1 s state is in good agreement with the reported result based on the Numerov approach. The exciton states are elongated along the x direction, while their radial nodes occur in the y direction, which leads to anomalous anisotropy in some excited states. The excitonic absorption spectra of monolayer BP possess highly anisotropic features and more peaks. The large anisotropy of the effective masses leads to the mixture of exciton states with different quantum numbers n and l , which results in highly nonhydrogenic and anisotropic features. These unusual excitonic and optical properties demonstrate the potential applications of monolayer BP in optoelectronics. Compared with my proposed diagonalization method, the variational method presented in the literatures is not a good approximation. My proposed variationally optimized diagonalization method based on a 2D nonorthogonal Laguerre basis is proven to be efficient and reliable in calculating highly accurate exciton states of anisotropic 2D materials . • A fully analytical expression of the matrix elements of the Hamiltonian is obtained. • The energy of 1 s state is in good agreement with the reported result based on the Numerov approach. • The states are elongated along the x direction while radial nodes occur in the y direction. • The excitonic absorption spectra possess highly anisotropic features and more peaks. • A 2D nonorthogonal Laguerre basis is efficient and reliable in calculating exciton states of anisotropic materials.

Regulation of electronic and optical properties of monolayer black phosphorus by co-doping B and Si

The electronic and optical properties of B or Si single-doped phosphorene and ones of B and Si co-doped phosphorene are computed and compared by first-principles calculations. By B doping, the bandgap of phosphorene decreases from 0.92 to 0.65 eV, while Si doping directly changes the system from a direct bandgap semiconductor to metal. Compared with pristine phosphorene, the optical absorption of Si-doped phosphorene is red shifted. The optical absorption of black phosphorus can be regulated by changing the distance and position between B and Si. Therefore, bandgap engineering can be used to directly tune the optical absorption of the phosphorene system by the co-doping of B and Si.

Interfacial contact and electronic properties in the heterojunction based on black phosphorus and borophene

We study the electronic properties of heterostructures based on monolayer black phosphorus (BP) and two types of borophene (HBoro and BoroΔ). The contact between BP and borophene results in the disappearance of Schottky barriers, indicates the metallization of BP. The BP/HBoro forms an n-type Schottky contact and BP/BoroΔ forms a p-type Schottky contact between the channels and electrodes. The edge modification of BP also affects the Schottky contact type and Schottky barrier heights. Moreover, it is found that the gate voltage can not only effectively modulate the Schottky barrier height but also change the Schottky contact type of BP/borophene structures. The ohmic contact can be achieved at some certain gate voltage. The results provide a promising route to design and fabricate tunable devices based on edge modified BP with borophene electrodes.