Anomalously low thermal conductivity of two-dimensional GaP monolayers: A comparative study of the group GaX (X = N, P, As)

TL;DR

This study reveals that 2D GaP monolayers exhibit unexpectedly low thermal conductivity due to buckling-induced phonon anharmonicity, contrasting with GaN and GaAs, and provides fundamental insights into phonon transport mechanisms in GaX materials.

Contribution

First-principles analysis of phonon transport in 2D GaX monolayers, highlighting the role of buckling and electron delocalization in thermal conductivity differences.

Findings

GaP has ultra-low thermal conductivity of 1.52 W/mK.

Buckling structure stabilizes GaP and GaAs, unlike planar GaN.

Strong phonon anharmonicity in GaP reduces thermal conductivity.

Abstract

With the successful synthesis of the two-dimensional (2D) gallium nitride (GaN) in a planar honeycomb structure, the phonon transport properties of 2D GaN have been reported. However, it remains unclear for the thermal transport in Ga-based materials by substituting N to other elements in the same main group, which is of more broad applications. In this paper, based on first-principles calculations, we performed a comprehensive study on the phonon transport properties of 2D GaX (X = N, P, and As) with planar or buckled honeycomb structures. The thermal conductivity of GaP (1.52 Wm-1K-1) is found unexpectedly ultra-low, which is in sharp contrast to GaN and GaAs despite their similar honeycomb geometry structure. Based on PJTE theory, GaP and GaAs stabilize in buckling structure, different from the planar structure of GaN. Compared to GaN and GaAs, strong phonon-phonon scattering is found in GaP due to the strongest phonon anharmonicity. Given electronic structures, deep insight is gained into the phonon transport that the delocalization of electrons in GaP is restricted due to the buckling structure. Thus, non-bonding lone pair electrons of P atoms induce nonlinear electrostatic forces upon thermal agitation, leading to increased phonon anharmonicity in the lattice, thus reducing thermal conductivity. Our study offers a fundamental understanding of phonon transport in GaX monolayers with honeycomb structure, which will enrich future studies of nanoscale phonon transport in 2D materials