Abstract
Low-symmetry layered materials such as black phosphorus (BP) have been revived recently due to their high intrinsic mobility and in-plane anisotropic properties, which can be used in anisotropic electronic and optoelectronic devices. Since the anisotropic properties have a close relationship with their anisotropic structural characters, especially for materials with low-symmetry, exploring new low-symmetry layered materials and investigating their anisotropic properties have inspired numerous research efforts. In this paper, we review the recent experimental progresses on low-symmetry layered materials and their corresponding anisotropic electrical transport, magneto-transport, optoelectronic, thermoelectric, ferroelectric, and piezoelectric properties. The boom of new low-symmetry layered materials with high anisotropy could open up considerable possibilities for next-generation anisotropic multifunctional electronic devices.
Highlights
Two dimensional (2D) layered materials with strong in-plane covalent bonds and weak out-of-plane van der Waals interactions span a very broad range of solids and exhibit extraordinary and unique layer-dependent physical properties a er the discovery of graphene.[1,2,3,4,5,6] Even though graphene has extremely large mobility and outstanding electron-transport properties, the absence of a band gap restricts its applications in electronic devices
People mainly focus on the in-plane isotropic behaviors in graphene and Transition metal dichalcogenides (TMDCs) because of their symmetric crystal structures until the rediscovery of lowsymmetry black phosphorus (BP)
It is known that reducing the symmetry of materials is generally associated with exceptional anisotropy in electronic aInternational Collaborative Laboratory of 2D Materials for Optoelectronics Science Technology of Ministry of Education, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060, China
Summary
Two dimensional (2D) layered materials with strong in-plane covalent bonds and weak out-of-plane van der Waals interactions span a very broad range of solids and exhibit extraordinary and unique layer-dependent physical properties a er the discovery of graphene.[1,2,3,4,5,6] Even though graphene has extremely large mobility and outstanding electron-transport properties, the absence of a band gap restricts its applications in (opto) electronic devices. Strong in-plane anisotropic transport properties of low-symmetry 2D materials are typically a result of the different energy band structure along the different in-plane directions of the layered crystal lattice, leading to drastically different carrier effective mass along the different crystal directions. Due to the anisotropy of transport properties offered by low-symmetry layered 2D materials, their optoelectronic, thermoelectric, piezoelectric, and ferroelectric properties should be dependent on the crystalline directions. Investigating the anisotropic electronic properties along different crystalline orientations in low-symmetry 2D materials can optimize the performance of eld effect transistors,[35] photodetectors,[36] thermoelectric devices,[15] piezoelectric devices,[37] ferroelectric devices,[38] and so on. The anisotropic electronic properties, e.g., optoelectronic, magneto-transport, thermoelectric, piezoelectric, and ferroelectric properties (Fig. 1) with the applications using them are introduced and discussed.
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