Transport Properties Of Black Phosphorus Research Articles

Strain and electronic properties at the van der Waals interface of phosphorus/boron nitride heterobilayers

We study the mechanical and electronic properties of heterobilayers composed of black phosphorus (BP) on hexagonal boron nitride (hBN) and of blue phosphorus (${\mathrm{P}}_{\mathrm{blue}}$) on hBN by means of ab initio density functional theory. Emphasis is put on how the stress applied on the constituent layers impact their structural and electronic properties. For this purpose, we adopt a specific scheme of structural relaxation which allows us to distinguish between the energy cost of distorting each layer and the gain in stacking them together. In most cases we find that the BP tends to contract along the softer armchair direction, as already reported for similar structures. This contraction can attain up to 5% of strain, which might deteriorate its very good transport properties along the armchair direction. To prevent this, we propose a twisted-bilayer configuration where the largest part of the stress applies on the zigzag axis, resulting in a lower impact on the transport properties of BP. We also investigated a ${\mathrm{P}}_{\mathrm{blue}}$/hBN bilayer. A peculiar hybridization between the valence states of the two layers lets us suggest that electron-hole pairs excited in the bilayer will exhibit a mixed character, with electrons localized solely in the ${\mathrm{P}}_{\mathrm{blue}}$ layer and holes spread onto the two layers.

Temperature-Dependent Transport in Ultrathin Black Phosphorus Field-Effect Transistors.

We studied the temperature-dependent transport properties of ultrathin black phosphorus (BP). We present measurements of BP Schottky barrier (SB) metal-oxide-semiconductor field-effect-transistors (MOSFETs) with various channel lengths, constructed from a single BP sample with nanoscale uniformity in thickness and width. The electrical characterization reveals a reversal in the temperature dependence of drain current as a function of gate voltage. This reversal indicates a transition in the charge conduction limiting mechanisms as the device is swept from the off-state into the on-state. In the off-state, charge transport is limited by thermionic emission over the energy barriers at the source/drain SB contacts, and drain current increases with temperature. In the on-state, carriers can easily tunnel across the SB at the contacts, and charge transport is limited by scattering in the channel. As a result, drain current decreases with temperature in the on-state, as scattering increases with temperature. Using Landauer transport theory, we derive a closed-form expression for thermionic emission current in SB-MOSFETs with two-dimensional channels. We use this expression to extract the SB height at metal contact interface with BP and demonstrate the impact of scattering on the extraction. We then use a comprehensive BP SB-MOSFET model to analyze on-state current as a function of temperature and demonstrate the effects of charged impurity and phonon scattering on the transport properties of BP through extractions of mobility at fixed carrier density.

Electrical transport properties of black phosphorus based field-effect transistor with Au/Co/MgO tunneling contacts

Black phosphorus (BP) has recently emerged as a promising two-dimensional direct bandgap semiconducting material. Here, we report the fabrication and the electrical transport measurements of the black phosphorus based field-effect transistor with the Au/Co/MgO as drain and source tunneling contacts. By modulating the back-gate voltage, the multilayer black phosphorus channel exhibits ambipolar characteristics (both n-type and p-type) and the conduction behavior can be switched from hole dominated to electron dominated transport region. In the hole dominated region, we have measured a minimum of Schottky barrier height of 37 meV for Au/Co/MgO contact on BP. Moreover, the transistor ON/OFF (Ion/Ioff) ratio is obtained as large as 107 at 20 K and 105 at 300 K. A systematic study of the temperature and the back-gate voltage dependent conduction properties has been performed to understand the modulation of band structure and the ambipolar behavior. The demonstration of high ON/OFF ratio and low Schottky barrier height by using Au/Co/MgO tunneling contacts reveals a promising potential for spintronics applications with multilayer black phosphorus field-effect transistor.

Two-carrier analyses of the transport properties of black phosphorus under pressure

We report on the electronic transport properties of black phosphorus and analyze them using a two-carrier model in a wide range of pressure up to 2.5 GPa. In a semiconducting state at 0.29 GPa, the remarkable nonlinear behavior in the Hall resistance is reasonably reproduced by assuming the coexistence of two kinds of holes with different densities and mobilities. On the other hand, two-carrier analyses of the magnetotransport properties above 1.01 GPa suggest the coexistence of high-mobility electron and hole carriers that have almost the same densities, i.e., nearly compensated semimetallic nature of black phosphorus. In the semimetallic state, analyses of both the two-carrier model and quantum oscillations indicate a systematic increase in the carrier densities as pressure increases. An observed sign inversion of Hall resistivity at low magnetic fields suggests the existence of high-mobility electrons $(\ensuremath{\sim}{10}^{5}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$, which is roughly ten times larger than that of holes, in the semimetallic black phosphorus. We conclude that the extremely large positive magnetoresistance that has been observed in the semimetallic state cannot be reproduced by a conventional two-carrier model.

Oxygen induced strong mobility modulation in few-layer black phosphorus

2D black phosphorus configured field-effect transistors generally show a hole-transport-dominated ambipolar characteristic, owing to the severely restricted electron mobility by air ambient. Here, we demonstrate the strongly modulated mobility of few-layer black phosphorus in contact with oxygen. Pure oxygen exposure can dramatically decrease the electron mobility of black phosphorus by over three orders of magnitudes without degrading the hole transport. In situ x-ray photoelectron spectroscopy characterization reveals the physisorption nature of oxygen on black phosphorus. Density functional theory calculations identify the unoccupied states of molecular oxygen physisorbed on few-layer black phosphorus, that serves as electron trap but not as hole trap, consistent with the aforementioned mobility modulation. In contrast, oxygen exposure upon light illumination exhibits a significant attenuation for both electron and hole transport, originating from the photoactivated oxidation of black phosphorus, as corroborated by in situ x-ray photoelectron spectroscopy measurements. Our findings clarify the predominant role of oxygen in modulating transport properties of black phosphorus, thereby providing deeper insight to the design of black phosphorus based complementary electronics.