/Tag: Phosphorene

Quantum Hall Effect in Electron-Doped Black Phosphorus Field-Effect Transistors. (arXiv:1809.07536v1 [cond-mat.mtrl-sci])

2018-09-21T02:29:26+00:00 September 21st, 2018|Categories: Publications|Tags: |

The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the 2D hole gas in black phosphorus has reached high carrier mobilities that led to the observation of the integer quantum Hall effect, the improvement in the sample quality of the 2D electron gas (2DEG) has however been only moderate; quantum Hall effect remained elusive. Here, we obtain high quality black phosphorus 2DEG by defining the 2DEG region with a prepatterned graphite local gate. The graphite local gate screens the impurity potential in the 2DEG. More importantly, it electrostatically defines the edge of the 2DEG, which facilitates the formation of well-defined edge channels in the quantum Hall regime. The improvements enable us to observe precisely quantized Hall plateaus in electron-doped black phosphorus FET. Magneto-transport measurements under high magnetic fields further revealed a large effective mass and an enhanced Land’e g-factor, which points to strong electron-electron interaction in black phosphorus 2DEG. Such strong interaction may lead to exotic many-body quantum states in the fractional quantum Hall regime.

Published in: "arXiv Material Science".

Channel Thickness Optimization for Ultrathin and 2-D Chemically Doped TFETs

2018-09-21T00:34:26+00:00 September 21st, 2018|Categories: Publications|Tags: , |

The 2-D material-based TFETs are among the most promising candidates for low-power electronics applications since they offer ultimate gate control and high-current drives that are achievable through small tunneling distances ($Lambda $ ) during the device operation. The ideal device is characterized by a minimized $Lambda $ . However, devices with the thinnest possible body do not necessarily provide the best performance. For example, reducing the channel thickness (${T}_{text {ch}}$ ) increases the depletion width in the source, which can be a significant part of the total $Lambda $ . Hence, it is important to determine the optimum ${T}_{text {ch}}$ for each channel material individually. In this paper, we study the optimum ${T}_{text {ch}}$ for three channel materials: WSe2, black phosphorus, and InAs using full-band self-consistent quantum transport simulations. To identify the ideal ${T}_{text {ch}}$ for each material at a specific doping density, a new analytic model is proposed and benchmarked against the numerical simulations.

Published in: "IEEE Transactions on Electron Devices".

Intrinsic Performance of Germanane Schottky Barrier Field-Effect Transistors

2018-09-21T00:34:21+00:00 September 21st, 2018|Categories: Publications|Tags: , |

Germanane (GeH), a hydrogenated germanium monolayer, is a new family of 2-D semiconductors, exhibiting promising potential for electronic device applications. Here, we investigate GeH Schottky barrier (SB) field-effect transistors (FETs) using atomistic quantum transport simulations. Our simulation results reveal that the ohmic-contact device with zero SB height ($Phi _{text {Bn}}$ ) exhibits ~20% lower ON-current than the metal-oxide-semiconductor (MOS) FET counterpart due to the inherent tunnel barrier at the metal–semiconductor junction. We also compare 14-nm-channel GeH and black phosphorus (BP) SBFETs with a finite SB height of $Phi _{text {Bn}} = 0.22$ eV for both devices. Our results show that GeH outperforms BP in the ON-state, but it can suffer from larger leakage current in the OFF-state. We further investigate the effect of barrier height in GeH SBFET by varying $Phi _{text {Bn}}$ from 0 eV to a half bandgap (0.78 eV). In general, as barrier height increases, both ON-current and the minimum leakage current are reduced. It is also observed that, with increasing SB height, intrinsic delay increases but the required energy per switching decreases, indicating the trade-off between the device speed and the energy dissipation. Our benchmarking of GeH SBFET against GeH and BP MOSFETs demonstrates that GeH generally outperforms BP in terms of energy-delay product (EDP). By performing careful engineering of SB height along with the device threshold voltage, we show that the minimum EDP of GeH SBFET can be as comparable as that of the MOSFET counterpart, suggesting great potential of GeH SBFETs for future switching

Published in: "IEEE Transactions on Electron Devices".

Complementary Black Phosphorus Nanoribbons Field-Effect Transistors and Circuits

2018-09-21T00:34:11+00:00 September 21st, 2018|Categories: Publications|Tags: |

This paper demonstrates a high-performance black phosphorus nanoribbons field-effect transistor (BPNR-FET) and systematically investigates methods for enhancing its anisotropic carrier transport. The BPNR-FET shows a strong dependence on crystal orientation in which the best mobility performance is achieved in armchair-oriented nanoribbons. A downscaling of nanoribbon width is shown to improve the short-channel effect owing to a better electrostatic gate control. Furthermore, hydrogenation is employed to effectively passivate the dangling bonds and heal the nanoribbon edge defects, leading to nearly hysteresis-free transfer properties. By virtue of bandgap and contact-metal workfunction engineering, n-type BPNR-FET is successfully demonstrated, which enables complementary inverter circuits to be simultaneously realized. This paper unravels the superior performance underscores a conceptually new BPNR-FET, paving the way toward the development of non-planar devices and integrated circuits based on 2-D materials platform.

Published in: "IEEE Transactions on Electron Devices".

Mobility Anisotropy in Black Phosphorus MOSFETs With HfO<sub>2</sub> Gate Dielectrics

2018-09-21T00:33:53+00:00 September 21st, 2018|Categories: Publications|Tags: |

Precise measurements of the mobility anisotropy along high-symmetry crystal axes in black phosphorus (BP) MOSFETs are reported. Locally back-gated BP MOSFETs with 13-nm HfO2 dielectric and channel length ranging from 0.3 to 0.7 $mu text{m}$ are fabricated. A single BP flake of a uniform thickness is exfoliated and etched along armchair (AC) and zigzag (ZZ) crystal axes, and the orientations are confirmed using optical and transmission electron microscopy analyses. The hole and electron mobilities along each direction are extracted using the transfer length method. The AC-to-ZZ hole mobility ratio is found to increase from 1.4 (1.5) to 2.0 (2.9) as the sheet concentration increased from $5.1times 10^{textsf {11}}$ to $1.9times 10^{textsf {12}}$ cm−2 at room temperature (77 K). The room-temperature electron mobility anisotropy is found to be similar to that for holes with an AC-to-ZZ mobility ratio increasing from 1.4 to 2.1 from $5.1times 10^{textsf {11}}$ to $1.9times 10^{textsf {12}}$ cm−2 though electrons showed only a very weak temperature dependence. A Boltzmann transport model is used to explain the concentration- and temperature-dependent mobility anisotropies which can be well described using a charge center scattering model.

Published in: "IEEE Transactions on Electron Devices".

Tuning the Electronic Structures and Transport Properties of Zigzag Blue Phosphorene Nanoribbons

2018-09-21T00:33:49+00:00 September 21st, 2018|Categories: Publications|Tags: |

In recent years, single-element 2-D atom crystal materials have aroused extensive interest in many applications. Blue phosphorus, successfully synthesized on Au (111) substrate by molecular beam epitaxy not long ago, shows unusual geometrical and electronic structures. We investigate the electronic structures and transport properties of zigzag blue phosphorene nanoribbons (ZBPNRs) by using a first-principles method, which can be obviously tuned via different groups (i.e., -H, -O, and -OH) passivation on both edges. The ZBPNRs-H and ZBPNRs-OH present a wide-gap semiconductor property, while the ZBPNRs-O are metallic. Interestingly, the current–voltage (${I}$ –${V}$ ) curves of ZBPNRs-O show a negative differential resistive (NDR) effect, which is independent on the ribbon width. The electric current through the ZBPNRs-O mainly flows along both the outside zigzag phosphorus chains through the P-P bond current. By modifying both the edges with various functional groups, the ZBPNRs can display some important functional characteristics and become a candidate of NDR devices.

Published in: "IEEE Transactions on Electron Devices".

A Single-Step, Electrochemical Synthesis of Nitrogen doped Blue Luminescent Phosphorene Quantum Dots

2018-09-19T14:33:28+00:00 September 19th, 2018|Categories: Publications|Tags: |

Chem. Commun., 2018, Accepted ManuscriptDOI: 10.1039/C8CC07266C, CommunicationManila Ozhukil Valappil, Monika Ahlawat, Vijayamohanan K Pillai, Subbiah AlwarappanHerein, we report a one-step strategy for the electrochemical synthesis of nitrogen doped blue luminescent phosphorene quantum dots (NPQDs) from black phosphorous at room temperature. Nitrogen percentage in NPQDs can…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Toward Ultimate Control of Terahertz Wave Absorption in Graphene. (arXiv:1712.01708v2 [physics.optics] UPDATED)

2018-09-17T00:30:21+00:00 September 17th, 2018|Categories: Publications|Tags: , |

It is commonly believed that weak light-matter interactions in low-mobility graphene dramatically limits tunability of graphene-based optoelectronic devices, such as tunable absorbers or switches. In this paper, we develop and use a simple circuit model to understand absorption in graphene sheets. In particular, we show that light interacts weakly also with very high-mobility graphene sheets and propose systematic design means to overcome these problems. The results have allowed us to demonstrate in the terahertz band that perfect absorption with excellent electrical tunability can be achieved within a wide span of mobility values which almost covers the whole range of ever reported room-temperature mobilities. Remarkably, concentrating on the most practical low-mobility graphene devices, we exemplify our theory with two cases: frequency-tunable and switchable absorbers with near 100% modulation efficiencies. Our work provides systematic and instructive insights into the design of highly tunable absorbers, without restrictions on graphene mobility. The design strategy and the developed analytical model can, in principle, be generalized to other wavelength regions from microwave to mid-infrared range, and other two-dimensional materials such as transition metal dichalcogenides (TMDs) and black phosphorus.

Published : "arXiv Mesoscale and Nanoscale Physics".

Pressure-induced phase transitions and superconductivity in a black phosphorus single crystal [Physics]

2018-09-15T02:31:39+00:00 September 15th, 2018|Categories: Publications|Tags: |

We report a thorough study of the transport properties of the normal and superconducting states of black phosphorus (BP) under magnetic field and high pressure with a large-volume apparatus that provides hydrostatic pressure to induce transitions from the layered A17 phase to the layered A7 phase and to the cubic…

Published in: "PNAS (Ahead)".

Tunable electronic and magneto-optical properties of monolayer arsenene: From $mathrm{G}{mathrm{W}}_{0}$ approximation to large-scale tight-binding propagation simulations

2018-09-11T16:33:12+00:00 September 11th, 2018|Categories: Publications|Tags: , |

Author(s): Jin Yu, Mikhail I. Katsnelson, and Shengjun YuanMonolayers of the group called VA elements have attracted great attention with the rising of black phosphorus. Here, we derive a simple tight-binding model for monolayer grey arsenic, referred to as arsenene (ML-As), based on the first-principles calculations within the partially self-consistent GW0…[Phys. Rev. B 98, 115117] Published Tue Sep 11, 2018

Published in: "Physical Review B".

Detecting the Major Charge-Carrier Scattering Mechanism in Graphene Antidot Lattices. (arXiv:1809.02160v1 [cond-mat.mes-hall])

2018-09-10T02:29:13+00:00 September 10th, 2018|Categories: Publications|Tags: , , |

Charge carrier scattering is critical to the electrical properties of two-dimensional materials such as graphene, transition metal dichalcogenide monolayers, black phosphorene, and tellurene. Beyond pristine two-dimensional materials, further tailored properties can be achieved by nanoporous patterns such as nano- or atomic-scale pores (antidots) across the material. As one example, structure-dependent electrical/optical properties for graphene antidot lattices (GALs) have been studied in recent years. However, detailed charge carrier scattering mechanism is still not fully understood, which hinders the future improvement and potential applications of such metamaterials. In this paper, the energy sensitivity of charge-carrier scattering and thus the dominant scattering mechanisms are revealed for GALs by analyzing the maximum Seebeck coefficient with a tuned gate voltage and thus shifted Fermi levels. It shows that the scattering from pore-edge-trapped charges is dominant, especially at elevated temperatures. For thermoelectric interests, the gate-voltage-dependent power factor of different GAL samples are measured as high as 509 at 400 K for a GAL with the square pattern. Such a high power factor is improved by more than one order of magnitude from the values for the state-of-the-art bulk thermoelectric materials. With their high thermal conductivities and power factors, these GALs can be well suitable for “active coolers” within electronic devices, where heat generated at the hot spot can be removed with both passive heat conduction and active Peltier cooling.

Published in: "arXiv Material Science".

Unraveling the not-so-large trion binding energy in monolayer black phosphorus

2018-09-07T16:33:33+00:00 September 7th, 2018|Categories: Publications|Tags: , |

Black phosphorus (bP) is a promising two-dimensional (2D) material for opto-electronic applications. Strongly bound excitons with binding energies up to 0.3 eV and remarkably large trion binding energies up to 100 meV have been observed for supported monolayer bP. Surprisingly, this trion binding energy is significantly larger than those found in other 2D materials (e.g. about 30 meV in transition metal dichalcogenides). This has previously been ascribed to the quasi-1D nature of bP. In this work we show, using first principles calculations, that the trion binding energy of bP is indeed large (80 meV) when referenced to the lowest bright exciton but only 30 meV when its energy is measured relative to the lowest dark exciton. Our analysis thus shows that the trion binding energy in bP is not larger than in other 2D materials, and the previous conclusions have to be understood incorporating the large splitting between the dark and bright excitons in bP. We also explore the effect …

Published in: "2DMaterials".

Theoretical studies of electronic transport in monolayer and bilayer phosphorene: A critical overview

2018-09-07T14:33:41+00:00 September 7th, 2018|Categories: Publications|Tags: |

Author(s): Gautam Gaddemane, William G. Vandenberghe, Maarten L. Van de Put, Shanmeng Chen, Sabyasachi Tiwari, Edward Chen, and Massimo V. FischettiRecent ab initio theoretical calculations of the electrical performance of several two-dimensional materials predict a low-field carrier mobility that spans several orders of magnitude (from 26000 to 35 cm2V−1s−1, for example, for the hole mobility in monolayer phosphorene) depending on the physical…[Phys. Rev. B 98, 115416] Published Fri Sep 07, 2018

Published in: "Physical Review B".

WSe 2 /Au vertical Schottky junction photodetector with low dark current and fast photoresponse

2018-09-06T10:34:05+00:00 September 6th, 2018|Categories: Publications|Tags: , |

Atomically thin two-dimensional materials including graphene, transition metal dichalcogenides, black phosphorus and so forth have been considered as promising channel medias for electronic and optoelectronic devices in the past few years. However, the poor photoresponse time and the large dark current are the two major issues which greatly block their applications. Here, we report a vertical Au–WSe 2 –ITO (indium tin oxide) Schottky junction photodetector with a broadband photoresponse from 550–950 nm and a stable photovoltaic responsivity of ∼0.1 A W −1 . The fast photoresponse of ∼50 μ s and low dark current of ∼1 pA are achieved at the vertical Au–WSe 2 –ITO photodetector. These results indicate that metal contact to a 2D material-based vertical Schottky junction can achieve an excellent photoelectric response.

Published in: "Nanotechnology".

Phosphorene quantum dot electronic properties and gas sensing. (arXiv:1809.01641v1 [cond-mat.mes-hall])

2018-09-06T04:30:18+00:00 September 6th, 2018|Categories: Publications|Tags: , |

Density functional theory calculations are performed on phosphorene quantum dots having different shapes and edge terminations to investigate their structure stability, electronic properties, and gas sensing ability. All the selected phosphorene dots, namely hexagonal and triangular flakes with armchair and zigzag terminations, have positive binding energies which insure their stability even though the bond lengths are much longer than those in the infinite phosphorene layer. It is found that all the selected hydrogen passivated quantum dots have a wide energy gap. In contrast, the partial passivation with sulfur decreases the gap. Moreover, it transforms the system from antiferromagnetic to ferromagnetic state. The energy gap of hexagonal zigzag cluster can be additionally tuned by electric field: narrowed by about 1.7 eV for hydrogenated or broadened by 0.25 eV for partially sulfurated edges. It is shown that phosphorene quantum dots successfully adsorb H2S, CH4, CO, NH3 gas molecules either on their edge or surface. The highest adsorption energy is obtained for NH3 molecule, when it is placed over the surface. This adsorption is alleviated by in-plane electric field and hindered by perpendicular field.

Published : "arXiv Mesoscale and Nanoscale Physics".

Tunnable rectifying performance of in-plane metal–semiconductor junctions based on passivated zigzag phosphorene nanoribbons

2018-09-05T10:34:03+00:00 September 5th, 2018|Categories: Publications|Tags: |

RSC Adv., 2018, 8,31255-31260DOI: 10.1039/C8RA05691A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.ShaoLong Su, Jian Gong, Zhi-Qiang FanUsing first principles density functional theory, we perform a systematic study of the band structures of passivated zigzag

Published in: "RSC Advances".

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