The strength of light-matter interaction is of central importance in photonics and optoelectronics. For many widely studied two-dimensional semiconductors, such as MoS2, the optical absorption due to exciton resonances increases with thickness. However, here we will show, few-layer black phosphorus exhibits an opposite trend. We determine the optical conductivity of few-layer black phosphorus with thickness down to bilayer by infrared spectroscopy. On the contrary to our expectations, the frequency-integrated exciton absorption is found to be enhanced in thinner samples. Moreover, the continuum absorption near the band edge is almost a constant, independent of the thickness. We will show such scenario is related to the quanta of the universal optical conductivity of graphene, with a prefactor originating from the band anisotropy.
Black phosphorus (BP) is a two-dimensional layered material composed of phosphorus atoms. Recently, it was demonstrated that external perturbations such as an electric field close the band gap in few-layer BP, and can even induce a band inversion, resulting in an insulator phase with a finite energy gap or a Dirac semimetal phase characterized by two separate Dirac nodes. At the transition between the two phases, a semi-Dirac state appears in which energy disperses linearly along one direction and quadratically along the other. In this work, we study the optical conductivity of few-layer BP us…
Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Though highly desirable, a comprehensive infrared characterization is still lacking. Here we report a systematic infrared study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer black phosphorus exhibits a thickness-dependent unique infrared spectrum with a series of absorption reson…
Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics. Here we report the anisotropic in-plane thermal conductivity of suspended few-layer black phosphorus measured by micro-Raman spectroscopy. The armchair and zigzag thermal conductivities are ~20 and ~40 W m$^{-1}$ K$^{-1}$ for black phosphorus films thicker than 15 nm, respectively, and decrease to ~10 and ~20 W m$^{-1}$ K$^{-1}$ as the film thickness is reduced, exhibiting significant anisotropy. The thermal conductivity anisotropic ratio is found to…
We propose and analyze the heterostructure comprising a black-arsenic-phosphorus layer (b-As$_{1-x}$P$_x$L) and a graphene layer (GL) integrated with a light-emitting diode (LED). The integrated b-As$_{1-x}$P$_x$L-GL-LED heterostructure can serve as an active part of the terahertz (THz) laser using the interband radiative transitions in the GL. The feasibility of the proposed concept is enabled by the combination of relatively narrow energy gap in the b-As$_{1-x}$P$_x$L and the proper band alignment with the GL. The operation of the device in question is associated with the generation of the e…
Black phosphorus is emerging as a promising semiconductor for electronic and optoelectronic applications. To study fundamental carrier properties, we performed ultrafast femtosecond pump-probe spectroscopy on thin film black phosphorus mechanically exfoliated on a glass substrate. Carriers (electrons and holes) were excited to high energy levels and the process of carrier relaxation through phonon emission and recombination was probed. We used a wide range of probing wavelengths up to and across the band gap to study the evolution of the relaxation dynamics at different energy levels. Our expe…
Black phosphorus has attracted great research interest due to its numerous applications in electronic devices, optoelectronic devices, energy storages and so on. Compared with the majority of two-dimensional materials, black phosphorus possesses a unique property, i.e. the strong in-plane anisotropy. All the properties reported so far, including its effective mass, electron mobility, light absorption, thermal conductivity and so on, have shown great anisotropy in the basal plane. This property renders black phosphorus unique applications not achievable with other two-dimensional materials. In …
Black phosphorus has attracted interest as a material for use in optoelectronic devices due to many favorable properties such as a high carrier mobility, field-effect, and a direct bandgap that can range from 0.3 eV in its bulk crystalline form to 2 eV for a single atomic layer. The low bandgap energy for bulk black phosphorus allows for direct transition photoabsorption that enables detection of light out to mid-infrared frequencies. In this work we characterize the room temperature optical response of a black phosphorus photoconductive detector at wavelengths ranging from 1.56 $μ$m to 3.75 $…
Black phosphorus (BP), a two-dimensional (2D) van der Waals layered material composed of phosphorus atoms, has been one of the most actively studied 2D materials in recent years due to its tunable energy band gap (tunable even to a negative value) and its highly anisotropic electronic structure. Depending on the sign of the band gap tuning parameter, few-layer BP can be in a gapped insulator phase, gapless Dirac semimetal phase, or gapless semi-Dirac transition point between the two phases. Using the fully anisotropic multiband Boltzmann transport theory, we systematically study the dc conduct…
Black phosphorus (BP) has emerged as a direct-bandgap semiconducting material with great application potentials in electronics, photonics, and energy conversion. Experimental characterization of the anisotropic thermal properties of BP, however, is extremely challenging due to the lack of reliable and accurate measurement techniques to characterize anisotropic samples that are micrometers in size. Here, we report measurement results of the anisotropic thermal conductivity of bulk BP along three primary crystalline orientations, using the novel time-resolved magneto-optical Kerr effect (TR-MOKE…
Atomically-thin black phosphorus (BP) is an emerging two dimensional (2D) material exhibiting bright photoluminescence in the near infrared. Coupling its radiation to photonic nanostructures will be an important step toward the realization of 2D material based nanophotonic devices that operate efficiently in the near infrared, which includes the technologically important optical telecommunication wavelength bands. In this letter, we demonstrate the optical coupling between atomically-thin BP and a 2D photonic crystal nanocavity. We employed a home-build dry transfer apparatus for placing a thi…
We investigate the electro-optic properties of black phosphorus (BP) thin films for optical modulation in the mid-infrared frequencies. Our calculation indicates that an applied out-of-plane electric field may lead to red-, blue-, or bidirectional shift in BP's absorption edge. This is due to the interplay between the field-induced quantum-confined Franz-Keldysh effect and the Pauli-blocked Burstein-Moss shift. The relative contribution of the two electro-absorption mechanisms depends on doping range, operating wavelength, and BP film thickness. For proof-of concept, simple modulator configura…
We examine the electronic properties of 2D electron gas in black phosphorus multilayers in the presence of a perpendicular magnetic field, highlighting the role of in-plane anisotropy on various experimental quantities such as ac magneto-conductivity, screening, and magneto-plasmons. We find that resonant structures in the ac conductivity exhibits a red-shift with increasing doping due to inter-band coupling, $γ$. This arises from an extra correction term in the Landau energy spectrum proportional to $n^2γ^2$ ($n$ is Landau index), up to second order in $γ$. We found also that Coulomb interact…
The mid-infrared (MIR) spectral range, pertaining to important applications such as molecular 'fingerprint' imaging, remote sensing, free space telecommunication and optical radar, is of particular scientific interest and technological importance. However, state-of-the-art materials for MIR detection are limited by intrinsic noise and inconvenient fabrication processes, resulting in high cost photodetectors requiring cryogenic operation. We report black arsenic-phosphorus-based long wavelength infrared photodetectors with room temperature operation up to 8.2 um, entering the second MIR atmosph…
The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic control of light propagation by an applied potential. While many materials have been shown to exhibit electrically tunable permittivity and dispersion, including transparent conducting oxides (TCOs) and III-V semiconductors and quantum wells, these materials are all optically isotropic in the propagation plane. In this work, we report the first known example of electrically tunable linear dichroism, observed here in few-layer black phosphorus (BP), which is a promisi…
The double carrier transport has been observed in thin film black phosphorus (BP) field effect transistor (FET) devices in highly electron doped region. BP thin films with typical thickness of 15 nm were encapsulated by hexagonal boron nitride (h-BN) thin films to avoid degradation by air exposure. Their Hall mobility has reached 5300 cm2/Vs and 5400 cm2/Vs at 4.2 K in the hole and electron doped regions, respectively. The gate voltage dependence of conductivity exhibits an anomalous shoulder structure in electron doped region. In addition, at gate voltages above the shoulder, the magnetoresis…
We report measurements of the infrared optical response of thin black phosphorus under field-effect modulation. We interpret the observed spectral changes as a combination of an ambipolar Burstein-Moss (BM) shift of the absorption edge due to band-filling under gate control, and a quantum confined Franz-Keldysh (QCFK) effect, phenomena which have been proposed theoretically to occur for black phosphorus under an applied electric field. Distinct optical responses are observed depending on the flake thickness and starting carrier concentration. Transmission extinction modulation amplitudes of mo…
Black phosphorus thin films might offer attractive alternatives to narrow gap compound semiconductors for optoelectronics across mid- to near-infrared frequencies. In this work, we calculate the optical conductivity tensor of multilayer black phosphorus thin films using the Kubo formula within an effective low-energy Hamiltonian. The optical absorption spectra of multilayer black phosphorus are shown to vary sensitively with thickness, doping, and light polarization. In conjunction with experimental spectra obtained from infrared absorption spectroscopy, we also discuss the role of interband c…
The attraction between electrons and holes in semiconductors forms excitons, which largely determine the optical properties of the hosting material, and hence the device performance, especially for low-dimensional systems. Mono- and few-layer black phosphorus (BP) are emerging two-dimensional (2D) semiconductors. Despite its fundamental importance and technological interest, experimental investigation of exciton physics has been rather limited. Here, we report the first systematic measurement of exciton binding energies in ultrahigh quality few-layer BP by infrared absorption spectroscopy, wit…
We propose and evaluate the heterostructure based on the graphene-layer (GL) with the lateral electron injection from the side contacts and the hole vertical injection via the black phosphorus layer (PL) (p$^+$PL-PL-GL heterostructure). Due to a relatively small energy of the holes injected from the PL into the GL (about 100 meV, smaller than the energy of optical phonons in the GL which is about 200 meV), the hole injection can effectively cool down the two-dimensional electron-hole plasma in the GL. This simplifies the realization of the interband population inversion and the achievement of …
The electronic structure of few-layer(FL) black phosphorus(BP) sensitively depends on the sample thickness, strain and doping. In this paper, we show that it is also vulnerable to air-exposure. The oxidation of BP caused by air-exposure gives several optical signatures, including the broadening of resonance peaks and increased Stokes shift between infrared (IR) absorption and photoluminescence (PL) peaks. More importantly, air exposure causes blue shifts of all resonance peaks in IR absorption and PL spectra, with more prominent effects for thinner samples and higher order subband transitions.…
In this study, we develop a systematic weak localization/antilocalization theory fully considering the anisotropy and Berry phase of the system, and apply it to various phases of few-layer black phosphorus (BP), which has a highly anisotropic electronic structure with an electronic gap size tunable even to a negative value. The derivation of a Cooperon ansatz for the Bethe-Salpeter equation in a general anisotropic system is presented, revealing the existence of various quantum interference effects in different phases of few-layer BP, including a crossover from weak localization to antilocaliz…
We study the quantum Hall effect of 2D electron gas in black phosphorus in the presence of perpendicular electric and magnetic fields. In the absence of a bias voltage, the external magnetic field leads to a quantization of the energy spectrum into equidistant Landau levels, with different cyclotron frequencies for the electron and hole bands. The applied voltage reduces the band gap, and eventually a semiconductor to semimetal transition takes place. This nontrivial phase is characterized by the emergence of a pair of Dirac points in the spectrum. As a consequence, the Landau levels are not e…
The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus (BP) by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10V/nm to 0.83V/nm. …
Black phosphorus has recently emerged as a promising material for high performance electronic and optoelectronic device for its high mobility, tunable mid-infrared bandgap and anisotropic electronic properties. Dynamical evolution of photo excited carriers and its induced change of transient electronic properties are critical for materials' high field performance, but remains to be explored for black phosphorus. In this work, we perform angle resolved transient reflection spectroscopy to study the dynamical evolution of anisotropic properties of black phosphorus under photo excitation. We find…
The travel of heat in insulators is commonly pictured as a flow of phonons scattered along their individual trajectory. In rare circumstances, momentum-conserving collision events dominate, and thermal transport becomes hydrodynamic. One of these cases, dubbed the Poiseuille flow of phonons, can occur in a temperature window just below the peak temperature of thermal conductivity. We report on a study of heat flow in bulk black phosphorus between 0.1 and 80 K. We find a thermal conductivity showing a faster than cubic temperature dependence between 5 and 12 K. Consequently, the effective phono…
Few-layer black phosphorus, a new elemental 2D material recently isolated by mechanical exfoliation, is a high-mobility layered semiconductor with a direct bandgap that is predicted to strongly depend on the number of layers, from 0.35 eV (bulk) to 2.0 eV (single-layer). Therefore, black phosphorus is an appealing candidate for tunable photodetection from the visible to the infrared part of the spectrum. We study the photoresponse of field-effect transistors (FETs) made of few-layer black phosphorus (3 nm to 8 nm thick), as a function of excitation wavelength, power and frequency. In the dark …
The potential of bulk black-phosphorus for thermoelectric applications has been experimentally studied. The Seebeck Coefficient (S) has been measured in the temperature range from 300 K to 385 K, finding a value of S = +335 +- 10 uV/K at room temperature (indicating a naturally occurring p-type conductivity). S increases with temperature, as expected for p-type semiconductors, which can be attributed to an increase of the charge carrier density. The electrical resistance drops up to a 40 % while heating in the studied temperature range. As a consequence, the power factor at 385 K is 2.7 times …
We investigate unusual surface plasmons polariton (SPP) propagation and light-matter interactions in ultrathin black phosphorus (BP) films, a 2D material that exhibits exotic electrical and physical properties due to its extremely anisotropic crystal structure. Recently, it has been speculated that the ultra-confined surface plasmons supported by BP may present various topologies of wave propagation bands, ranging from anisotropic elliptic to hyperbolic, across the mid- and near-infrared regions of the electromagnetic spectrum. By carefully analyzing the natural nonlocal anisotropic optical co…
Recently, it was demonstrated that a graphene/dielectric/metal configuration can support acoustic plasmons, which exhibit extreme plasmon confinement an order of magnitude higher than that of conventional graphene plasmons. Here, we investigate acoustic plasmons supported in a monolayer and multilayers of black phosphorus (BP) placed just a few nanometers above a conducting plate. In the presence of a conducting plate, the acoustic plasmon dispersion for the armchair direction is found to exhibit the characteristic linear scaling in the mid- and far-infrared regime while it largely deviates fr…
The conductivity of graphite is analytically evaluated in the range of 0.1-1.5 eV, where the electron relaxation processes can be neglected, and the low energy excitations at the "Dirac" points are most essential. The value of conductivity calculated per one graphite layer is close to the universal conductivity of graphene. The features of the conductivity are explained in terms of singularities of the electron dispersion in graphite.
Two-dimensional materials and their heterostructures have emerged as a new class of materials for not only fundamental physics but also for electronic and optoelectronic applications. Black phosphorus (BP) is a relatively new addition to this class of materials. Its strong in plane anisotropy makes BP a unique material to make conceptually new type of electronic devices. However, the global density of states (DOS) of BP in device geometry has not been measured experimentally. Here we report the quantum capacitance measurements together with conductance measurements on a hBN protected few layer…
Nonlocal electrodynamics of two-dimensional anisotropic magneto-plasmons
Aeronautics Institute of Technology（航空技术学院）；University of Southern Denmark（南丹麦大学）；Universidade Federal do Ceará（塞阿拉联邦大学）；University of Antwerp（安特卫普大学）；Danish Institute for Advanced Study, University of Southern Denmark（南丹麦大学丹麦高等研究院）；Universidade do Minho（米尼奥大学）
We study the electronic and optical properties of single- and bilayer black phosphorus with shortand long-range defects by using the tight-binding propagation method. Both types of defect states are localized and induce a strong scattering of conduction states reducing significantly the charge carrier mobility. In contrast to properties of pristine samples, the anisotropy of defect-induced optical excitations is suppressed due to the isotropic nature of the defects. We also investigate the Landau level spectrum and magneto-optical conductivity, and find that the discrete Landau levels are subl…
Few-layer and thin film forms of layered black phosphorus (BP) have recently emerged as a promising material for applications in high performance nanoelectronics and infrared optoelectronics. Layered BP thin film offers a moderate bandgap of around 0.3 eV and high carrier mobility, leading to transistors with decent on-off ratio and high on-state current density. Here, we demonstrate the gigahertz frequency operation of black phosphorus field-effect transistors for the first time. The BP transistors demonstrated here show excellent current saturation with an on-off ratio exceeding 2000. We ach…
Black phosphorus presents a very anisotropic crystal structure, making it a potential candidate for hyperbolic plasmonics, characterized by a permittivity tensor where one of the principal components is metallic and the other dielectric. Here we demonstrate that atomically thin black phosphorus can be engineered to be a hyperbolic material operating in a broad range of the electromagnetic spectrum from the entire visible spectrum to ultraviolet. With the introduction of an optical gain, a new hyperbolic region emerges in the infrared. The character of this hyperbolic plasmon depends on the int…
We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, n^{\rm C}_i. We find an anomalous enhancement of the conductivity …
Semi-metallic graphene and semiconducting monolayer transition metal dichalcogenides (TMDCs) are the two-dimensional (2D) materials most intensively studied in recent years. Recently, black phosphorus emerged as a promising new 2D material due to its widely tunable and direct bandgap, high carrier mobility and remarkable in-plane anisotropic electrical, optical and phonon properties. However, current progress is primarily limited to its thin-film form, and its unique properties at the truly 2D quantum confinement have yet to be demonstrated. Here, we reveal highly anisotropic and tightly bound…
In this study, a newly pillared black phosphorene hybrid nanostructures (PBP) is constructed with its thermal stability as well as thermal conductivity are studied by performing equilibrium molecular dynamics simulation (EMD). The results show that the curvature of the nanotube and the intense thermal vibration of the atoms are responsible for the failure of PBP at finite temperature simultaneously. The calculation of normalized HCACF and running thermal conductivities (RTC) as a function of correlation time demonstrate that thermal conductivities decreases with the temperature significantly, …
We present far-infrared (FIR) photo-conductivity measurements for a two-dimensional electron gas in an array of nano-structured antidots. We detect, resistively and spectrally resolved, both the magnetoplasmon and the edge-magnetoplasmon modes. Temperature-dependent measurements demonstrates that both modes contribute to the photo resistance by heating the electron gas via resonant absorption of the FIR radiation. Influences of spin effect and phonon bands on the collective excitations in the antidot lattice are observed.
Hyperbolic polaritons exhibit large photonic density of states and can be collimated in certain propagation directions. The majority of hyperbolic polaritons are sustained in man-made metamaterials. However, natural-occurring hyperbolic materials also exist. Particularly, natural in-plane hyperbolic polaritons in layered materials have been demonstrated in MoO3 and WTe2, which are based on phonon and plasmon resonances respectively. Here, by determining the anisotropic optical conductivity (dielectric function) through optical spectroscopy, we predict that monolayer black phosphorus naturally …
Atomic layers of Black Phosphorus (BP) present unique opto-electronic properties dominated by a direct tunable bandgap in a wide spectral range from visible to mid-infrared. In this work, we investigate the infrared photoluminescence of BP single crystals at very low temperature. Near-bandedge recombinations are observed at 2 K, including dominant excitonic transitions at 0.276 eV and a weaker one at 0.278 eV. The free-exciton binding energy is calculated with an anisotropic Wannier-Mott model and found equal to 9.1 meV. On the contrary, the PL intensity quenching of the 0.276 eV peak at high …
We investigate the effect of Rashba spin-orbit coupling (SOC) on the optoelectronic properties of n- and p-type monolayer MoS2. The optical conductivity is calculated within the Kubo formalism. We find that the spin-flip transitions enabled by the Rashba SOC result in a wide absorption window in the optical spectrum. Furthermore, we evaluate the effects of the polarization direction of the radiation, temperature, carrier density, and the strength of the Rashba spin-orbit parameter on the optical conductivity. We find that the position, width, and shape of the absorption peak or absorption wind…
Layered two-dimensional materials have shown novel optoelectronic properties and are well suited to be integrated in planar photonic circuits. For example, graphene has been utilized for wideband photodetection. Because graphene lacks a band gap, however, graphene photodetectors suffer from very high dark current. In contrast, layered black phosphorous, the latest addition to the family of 2D materials, is well-suited for photodetector applications due to its narrow but finite band gap. Here, we demonstrate a gated multilayer black phosphorus photodetector integrated on a silicon photonic wave…
Through infrared spectroscopy, we systematically study the pressure effect on electronic structures of few-layer black phosphorus (BP) with layer number ranging from 2 to 13. We reveal that the pressure-induced shift of optical transitions exhibits strong layer-dependence. In sharp contrast to the bulk counterpart which undergoes a semiconductor to semimetal transition under ~1.8 GPa, the bandgap of 2 L increases with increasing pressure until beyond 2 GPa. Meanwhile, for a sample with a given layer number, the pressure-induced shift also differs for transitions with different indices. Through…
We report the quasiparticle band gap, excitons, and highly anisotropic optical responses of few-layer black phosphorous (phosphorene). It is shown that these new materials exhibit unique many-electron effects; the electronic structures are dispersive essentially along one dimension, leading to particularly enhanced self-energy corrections and excitonic effects. Additionally, within a wide energy range, including infrared light and part of visible light, few-layer black phosphorous absorbs light polarized along the structure's armchair direction and is transparent to light polarized along the z…
Anisotropy refers to the property of a material exhibiting directionally dependent features. In this paper, we introduce black phosphorous (BP), the most stable allotrope of phosphorus in layered orthorhombic structure with a bandgap of 0.3 eV in bulk, as a unique 2D material in which electrons, phonons and their interactions with photons behave in a highly anisotropic manner within the plane of the layers. The unique anisotropic nature of BP thin films is revealed using angle-resolved Raman and infrared spectroscopies, together with angle-resolved transport study. For 15 nm thick BP, we measu…
The origin of phonon thermal Hall Effect (THE) observed in a variety of insulators is yet to be identified. Here, we report on the observation of a thermal Hall conductivity in a non-magnetic elemental insulator, with an amplitude exceeding what has been previously observed. In black phosphorus (BP), the longitudinal ($κ_{ii}$), and the transverse, $κ_{ij}$, thermal conductivities peak at the same temperature and at this peak temperature, the $κ_{ij}/κ_{jj}/B $ is $\approx 10^{-4}$-$10^{-3}$ T$^{-1}$. Both these features are shared by other insulators displaying THE, despite an absolute amplit…
Artificial semiconductor heterostructures played a pivotal role in modern electronic and photonic technologies, providing a highly effective mean for the manipulation and control of carriers, from the visible to the far-infrared. Despite the exceptional versatility, they commonly require challenging epitaxial growth procedures due to the need of clean and abrupt interfaces, which proved to be a major obstacle for the realization of room-temperature (RT), high-efficiency devices, like source, detectors or modulators. The discovery of graphene and the related fascinating capabilities have trigge…
Two-dimensional materials supporting deep-subwavelength plasmonic modes can also exhibit strong magneto-optical responses. Here, we theoretically investigate magnetoplasmons (MPs) in monolayer black phosphorus (BP) structures under moderate static magnetic fields. We consider three different structures, namely, a continuous BP monolayer, an edge formed by a semi-infinite sheet, and finally, a triangular wedge configuration. Each of these structures shows strongly anisotropic magneto-optical responses induced both by the external magnetic field and by the intrinsic anisotropy of the BP lattice.…
Using first principles calculations we showed that the electronic and optical properties of single layer black phosphorus (BP) depend strongly on the applied strain. Due to the strong anisotropic atomic structure of BP, its electronic conductivity and optical response are sensitive to the magnitude and the orientation of the applied strain. We found that the inclusion of many body effects is essential for the correct description of the electronic properties of monolayer BP; for example while the electronic gap of strainless BP is found to be 0.90 eV by using semilocal functionals, it becomes 2…
Chemical doping of bulk black phosphorus is a well-recognized way to reduce surface oxidation and degradation. Here, we report on the fabrication of terahertz frequency detectors consisting of an antenna-coupled field-effect transistor (FET) with an active channel of Se-doped black phosphorus. Our devices show a maximum room-temperature hole mobility of 1780 cm2V-1s-1 in a SiO2-encapsulated FET. A room-temperature responsivity of 3 V/W was observed, with a noise-equivalent power of 7 nWHz-1/2 at 3.4 THz, comparable with the state-of-the-art room-temperature photodetectors operating at the same…
Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron spin. While graphene is very promising for spin communication due to its extraordinary electron mobility, the lack of a band gap restricts its prospects for semiconducting spin devices such as spin diodes and bipolar spin transistors. The recent emergence of 2D semiconductors could help overcome this basic challenge. In this letter we report the first important step towards making 2D semiconductor spin devices. We have fabricated a spin valve based on ultra-…
The possibility of hybridizing collective electronic motion with mid-infrared (mid-IR) light to form surface polaritons has made van der Waals layered materials a versatile platform for extreme light confinement and tailored nanophotonics. Graphene and its heterostructures have attracted particular attention because the absence of an energy gap allows for plasmon polaritons to be continuously tuned. Here, we introduce black phosphorus (BP) as a promising new material in surface polaritonics that features key advantages for ultrafast switching. Unlike graphene, BP is a van der Waals bonded semi…
Unencapsulated, exfoliated black phosphorus (BP) flakes are found to chemically degrade upon exposure to ambient conditions. Atomic force microscopy, electrostatic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are employed to characterize the structure and chemistry of the degradation process, suggesting that O2 saturated H2O irreversibly reacts with BP to form oxidized phosphorus species. This interpretation is further supported by the observation that BP degradation occurs more rapidly on hydrophobic octadecy…
