Giant Phononic Anisotropy and Unusual Anharmonicity of Phosphorene: Interlayer Coupling and Strain Engineering

TL;DR

This study reveals that monolayer phosphorene exhibits significant phononic anisotropy opposite to its electronic anisotropy, which can be effectively tuned by strain, impacting its potential in nanoelectronic and thermoelectronic applications.

Contribution

The paper provides a comprehensive first-principles analysis of phononic anisotropy and anharmonicity in phosphorene, uncovering hidden directions and strain tunability not previously reported.

Findings

Monolayer phosphorene has giant phononic anisotropy opposite to its electronic anisotropy.

Strain engineering can effectively tune phononic properties and anharmonicity directions.

Identification of 'hidden' phonon directions with minimal anharmonicity.

Abstract

Phosphorene, an emerging elemental two-dimensional (2D) direct band gap semiconductor with fascinating structural and electronic properties distinctively different from other 2D materials such as graphene and MoS2, is promising for novel nanoelectronic and optoelectronic applications. Phonons, as one of the most important collective excitations, are at the heart for the device performance, as their interactions with electrons and photons govern the carrier mobility and light-emitting efficiency of the material. Here, through a detailed first-principles study, it is demonstrated that monolayer phosphorene exhibits a giant phononic anisotropy, and remarkably, this anisotropy is squarely opposite to its electronic counterpart and can be tuned effectively by strain engineering. By sampling the whole Brillouin zone for the mono-layer phosphorene, several "hidden" directions are found, along which small-momentum phonons are "frozen" with strain and possess the smallest degree of anharmonicity. Unexpectedly, these "hidden" directions are intrinsically different from those usually studied armchair and zigzag directions. Light is also shed on the anisotropy of interlayer coupling of few-layer phosphorene by examining the rigid-layer vibrations. These highly anisotropic and strain-tunable characteristics of phosphorene offer new possibilities for its applications in thermal management, thermoelectronics, nanoelectronics and phononics.