First-Principles Study of the Phonon Lifetime and Low Lattice Thermal of γ-GeSe: A Comparative

Germanium selenide (GeSe) is a unique two-dimensional (2D) material showing various polymorphs stable at ambient conditions. Recently, a new phase with a layered hexagonal lattice (gamma-GeSe) was synthesized with ambient stability and extraordinary electronic conductivity, even higher than that of graphite, while its monolayer is semiconducting. In this work, using first-principles derived force constants and the Boltzmann transport theory, we explore the lattice thermal conductivity (kappa(l)) of monolayer gamma-GeSe, together with a comparison with monolayer alpha-GeSe and beta-GeSe. The kappa(l) of the gamma-phase is relatively low (5.50 W/mK), comparable with those of alpha- and beta-phases. The acoustic branches in alpha-GeSe are well separated from the optical branches, limiting scattering channels in the phase space, while for beta-GeSe and gamma-GeSe, the acoustic branches are resonant with the low-frequency optical branches, facilitating more phonon-phonon scattering. For gamma-GeSe, the cumulative kappa(l) is isotropic and the phononic representative mean free path (rMFP) is the shortest (17.07 nm) among the three polymorphs, indicating that the.l of the gamma-phase is less likely to be affected by the size of the sample, while for gamma-GeSe, the cumulative kappa(l) grows slowly with the mean free path and the rMFP is longer (up to 20.56 and 35.94 nm along zigzag and armchair directions, respectively), showing a stronger size dependence of kappa(l). Our work suggests that GeSe polymorphs with overall low thermal conductivity are promising contenders for thermoelectric and thermal management applications.

Automated summary

Germanium selenide (GeSe) is a unique two-dimensional material with different stable polymorphs. The recently synthesized gamma-GeSe phase exhibits extraordinary electronic conductivity, higher than graphite, while its monolayer is a semiconductor. The various polymorphs of GeSe have overall low thermal conductivity, making them promising for thermoelectric and thermal management applications.