Strain‐Engineered Ultrahigh Mobility in Phosphorene for Terahertz Transistors

Fang, Ruhao; Cui, Xiangyuan; Khan, Mansoor A.; Stampfl, Catherine; Ringer, Simon P.; Zheng, Rongkun

doi:10.1002/aelm.201800797

Cited by 20 publications

(17 citation statements)

References 51 publications

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“…We stress that what is suggested here is at variance with recent theoretical studies that have proposed strain as a way to enhance mobility in various 2D materials [43][44][45][46][47][48][49][50][51] . These studies neglect intervalley scattering and consider the effect of strain on effective masses and, partially, on the intravalley scattering.…”

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confidence: 55%

Valley-Engineering Mobilities in Two-Dimensional Materials

et al. 2019

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Two-dimensional materials are emerging as a promising platform for ultrathin channels in fieldeffect transistors. To this aim, novel high-mobility semiconductors need to be found or engineered. While extrinsic mechanisms can in general be minimized by improving fabrication processes, the suppression of intrinsic scattering (driven e.g. by electron-phonon interactions) requires to modify the electronic or vibrational properties of the material. Since intervalley scattering critically affects mobilities, a powerful approach to enhance transport performance relies on engineering the valley structure. We show here the power of this strategy using uniaxial strain to lift degeneracies and suppress scattering into entire valleys, dramatically improving performance. This is shown in detail for arsenene, where a 2% strain stops scattering into 4 of the 6 valleys, and leads to a 600% increase in mobility. The mechanism is general and can be applied to many other materials, including in particular the isostructural antimonene and blue phosphorene. :1902.11209v2 [cond-mat.mtrl-sci] FIG. 1. Graphical Abstract arXiv

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confidence: 55%

Valley-Engineering Mobilities in Two-Dimensional Materials

et al. 2019

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“…Our calculated results, combined with experimental high-spatial-resolution Raman scattering experiments, aid in a qualitative understanding of the complicated inhomogeneous and anisotropic strain distributions in few-layered phosphorene. Since strain is predicted to be an efficient tuning tool for bandgap , and carrier mobility, we expect our results to be of use also for the manufacture of materials with desired electronic properties via strain- or layer-engineering.…”

Section: Discussionmentioning

confidence: 94%

“…We find that the Raman modes exhibit a qualitatively complex strain response, which is quantitatively strong. Furthermore, in addition to strongly anisotropic excitons, 6 electron mobility, 28 and thermal conductivity, 29 strong anisotropy is also found in vibrational properties, which yields qualitatively very different responses to strains applied in the AC and ZZ directions. Indeed, our simulations predict a significant modification of HF vibrational properties for compressive strains in excess of 2% applied in the ZZ direction.…”

Section: Discussionmentioning

confidence: 99%

“…In addition to the in-plane strain, the effect of ripples and wrinkles with significant out-of-plane deformations has also been studied , and their strongly anisotropic effect on electronic properties and the chemical activity of phosphorene is predicted . A wealth of properties under strain has been reported in FLP such as topological phase transition from normal to the quantum-spin Hall state, onset of superconductivity, a complex dependence of the bandgap ranging from metallic to semiconducting and featuring both direct and indirect bandgaps in single- and few-layered phosphorene, − a negative Poisson’s ratio, a strain-engineered ultrahigh carrier mobility, strain-modulated thermal conductivity, or funneling of excitons in MoS 2 toward the point of applied strain upon illumination …”

Section: Introductionmentioning

confidence: 99%

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Raman Activity of Multilayer Phosphorene under Strain

2019

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Using computational tools, we study the behavior of activities of lattice vibrational Raman modes in few-layered phosphorene of up to four layers subjected to a uniaxial strain of −2 to +6% applied in the armchair and zigzag directions. We study both high- and low-frequency modes and find very appreciable frequency shifts in response to the applied strain of up to ≈20 cm–1. The Raman activities are characterized by Ag2/Ag1 activity ratios, which provide very meaningful characteristics of functionalization via layer- and strain-engineering. The ratios exhibit a pronounced vibrational anisotropy, namely a linear increase with the applied armchair strain and a highly nonlinear behavior with a strong drop of the ratio with the strain applied along the zigzag direction. For the low-frequency modes, which are Raman active exclusively in few-layered systems, we find the breathing interlayer modes of primary importance due to their strong activities. For few-layered structures with a thickness ≥4, a splitting of the breathing modes into a pair of modes with complementary activities is found, with the lower frequency mode being strain activated. Our calculated database of results contains full angular information on activities of both low- and high-frequency Raman modes. These results, free of experimental complexities, such as dielectric embedding, defects, and size and orientation of the flakes, provide a convenient benchmark for experiments. Combined with high-spatial-resolution Raman scattering experiments, our calculated results will aid in the understanding of the complicated inhomogeneous strain distributions in few-layered phosphorene or the manufacture of materials with desired electronic properties via strain- or layer-engineering.

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“…To examine the energy stability of 2D FM FeCl, we calculated its cohesive energy, which is defined as E coh = (2 × E Fe + 2 × E Cl − E FeCl )/4; E Fe , E Cl , and E FeCl are the total energies of a single Fe atom, Cl atom, and 2D FeCl unit cell, respectively. The calculated cohesive energy of 2D FeCl is 3.71 eV atom −1 , and it is smaller than that of graphene monolayer (7.863 eV atom −1 ); [ 46 ] however, it is larger than that of phosphorene monolayer (3.61 eV atom −1 ), [ 47 ] which indicates that 2D FeCl is stable and it is possible to synthesize it experimentally. Based on the Heisenberg model, the Curie temperature T C can be obtained from the mean‐field approximation with the relations

J = E_{ex} / (2 z S^{2})

[ 48 ] and

\frac{3}{2} k_{normalB} T_{normalC} = - J

, where E ex is the exchange energy and it is equal to the minimal energy difference between the FM and AFM states, z is the number of nearest magnetic atoms, S is the spin angular momentum of each magnetic atom, and k B is the Boltzmann constant.…”

Section: Figurementioning

confidence: 99%

Valley Polarization in Monolayer Ferromagnetic FeCl: A First‐Principles Study

Zou

Sun

et al. 2020

Physica Rapid Research Ltrs

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Valleytronics has gradually attracted people's attention for providing new degrees of freedom to future electronic devices. Herein, it is proposed that valley polarization can be realized in 2D ferromagnetic FeCl with a square lattice. The first‐principles calculations without spin–orbital coupling (SOC) show that 2D FeCl is a spin‐polarized semimetal material, and the crossing points around the Fermi level are protected by mirror symmetry. When considering SOC, local bandgaps open around the Fermi level, and further calculations reveal that the Berry curvatures are opposite in sign around these gaps along with different high‐symmetry directions. By integrating the Berry curvature around these local extreme points, the Chern numbers of two valleys are ≈ −1/4 and 1/4, respectively, and the corresponding valley Chern number Cv is approximately equal to 1/2. This indicates that FeCl has the potential to realize the valley Hall effect (VHE) and will be a promising material in future valleytronics.

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Strain‐Engineered Ultrahigh Mobility in Phosphorene for Terahertz Transistors

Cited by 20 publications

References 51 publications

Valley-Engineering Mobilities in Two-Dimensional Materials

Valley-Engineering Mobilities in Two-Dimensional Materials

Raman Activity of Multilayer Phosphorene under Strain

Valley Polarization in Monolayer Ferromagnetic FeCl: A First‐Principles Study

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