Performance of α-, β- and γ-GeSe Monolayers for Near-Field Radiative Heat Transfer: An Ab Initio Study

In this work, the performance of three polymorphs of monolayer GeSe for near-field radiative heat transfer (NFRHT) applications is compared. The α, β, and γ phases of this interesting and novel two-dimensional (2D) semiconductor have been extensively investigated in many aspects and are promising materials for applications in NFRHT. While the performance of the α and β phases has already been investigated separately in the literature, no consistent and systematic comparison between the performance of the three phases has been performed. For a consistent comparison, the relevant physical parameters, like the effective electron masses and optical conductivities, were calculated using density functional theory. To increase the heat flux, the monolayers are assumed to be n-doped. It was concluded that despite some striking differences in their optical conductivities, which can vary from isotropic to highly anisotropic, the three phases can deliver similar maximum heat fluxes. This finding contradicts what is usually expected: that highly anisotropic 2D materials that can sustain hyperbolic plasmon-polaritons can be expected to deliver larger heat transfers compared to nonhyperbolic materials. This result evidence that other physical properties of real materials can be more relevant for optimizing the NFRHT.