[Paper Review] Black Arsenic: A Layered Semiconductor with Extreme in-plane Anisotropy

Yabin Chen, Kai Chen+19 more|arXiv (Cornell University)|May 1, 2018

2D Materials and ApplicationsMaterials Science1 references4 citations

TL;DR

This study identifies black arsenic (b-As) as a novel layered semiconductor exhibiting extreme in-plane electronic, thermal, and electrical anisotropy between its armchair (AC) and zigzag (ZZ) crystallographic directions. Through systematic characterization of single crystals, the authors demonstrate that b-As displays higher or comparable anisotropy ratios than any known 2D material, enabling new opportunities in anisotropic nanoelectronics and quantum device design.

ABSTRACT

Two-dimensional (2D) layered materials emerge in recent years as a new platform to host novel electronic, optical or excitonic physics and develop unprecedented nanoelectronic and energy applications. By definition, these materials are strongly anisotropic between within the basal plane and cross the plane. The structural and property anisotropies inside their basal plane, however, are much less investigated. Herein, we report a rare chemical form of arsenic, called black-arsenic (b-As), as an extremely anisotropic layered semiconductor. We have performed systematic characterization on the structural, electronic, thermal and electrical properties of b-As single crystals, with particular focus on its anisotropies along two in-plane principle axes, armchair (AC) and zigzag (ZZ). Our analysis shows that b-As exhibits higher or comparable electronic, thermal and electric transport anisotropies between the AC and ZZ directions than any other known 2D crystals. Such extreme in-plane anisotropies are able to potentially implement novel ideas for scientific research and device applications.

Motivation & Objective

• To explore the structural and electronic properties of black arsenic (b-As), a rare allotropic form of arsenic, as a potential layered semiconductor with strong in-plane anisotropy.
• To systematically characterize the anisotropic transport, thermal, and electronic behavior of b-As single crystals along the armchair (AC) and zigzag (ZZ) crystallographic directions.
• To determine whether b-As exhibits extreme anisotropy surpassing that of other known 2D materials, particularly in electronic and thermal transport properties.
• To evaluate the potential of b-As for novel device applications based on its pronounced in-plane anisotropy.

Proposed method

• Synthesis of high-quality single crystals of black arsenic (b-As) via vapor transport methods.
• Use of angle-resolved photoemission spectroscopy (ARPES) to map the electronic band structure and confirm its semiconducting nature.
• Measurement of electrical transport properties along the AC and ZZ directions to quantify in-plane anisotropy in conductivity and carrier mobility.
• Thermal conductivity measurements along the two in-plane crystallographic axes to assess anisotropy in heat transport.
• Structural characterization using X-ray diffraction and transmission electron microscopy to confirm the layered orthorhombic crystal structure of b-As.
• Theoretical analysis to correlate observed anisotropy with the underlying electronic band dispersion and Fermi surface geometry.

Experimental results

Research questions

• RQ1 Does black arsenic (b-As) exhibit significant in-plane anisotropy in its electronic band structure and transport properties along the armchair and zigzag directions?
• RQ2 How does the electrical conductivity of b-As vary between the armchair and zigzag crystallographic axes, and what is the magnitude of the anisotropy ratio?
• RQ3 To what extent does the thermal conductivity of b-As differ between the AC and ZZ directions, and how does it compare to other 2D semiconductors?
• RQ4 Can the extreme anisotropy in b-As be attributed to its unique layered orthorhombic crystal structure and electronic band dispersion?
• RQ5 What is the potential of b-As for future anisotropic nanoelectronic or thermoelectric devices based on its measured anisotropic transport properties?

Key findings

• Black arsenic (b-As) exhibits a pronounced in-plane anisotropy in electrical transport, with anisotropy ratios in conductivity and carrier mobility exceeding those of most known 2D semiconductors.
• The electronic band structure of b-As, as revealed by ARPES, confirms a semiconducting gap with strong anisotropy in effective mass and Fermi velocity along the armchair and zigzag directions.
• Thermal conductivity measurements show a significant anisotropy between the AC and ZZ directions, indicating directional heat flow control potential.
• The anisotropy in electrical and thermal transport in b-As surpasses or matches that of other 2D materials like black phosphorus, establishing it as a leading candidate for anisotropic device applications.
• The layered orthorhombic crystal structure of b-As is directly linked to its extreme in-plane anisotropy, with structural distortion amplifying electronic and transport anisotropy.
• b-As demonstrates a high degree of anisotropy in both electronic and thermal transport, suggesting potential for use in anisotropic transistors, thermoelectric devices, and spintronic applications.