Structural, electronic, vibrational, and thermoelectric properties of Janus Ge2PX(X=N,As,Sb, and Bi) monolayers

Abstract

Two-dimensional (2D) Janus systems have garnered significant scientific interest owing to their novel properties and potential applications. The growing interest in these materials is driven by the idea that their structural asymmetry offers unprecedented opportunities for enhancing thermoelectric performance and unlocking groundbreaking advancements in energy conversion and waste heat utilization. In this context, we present a comprehensive study on the structural, vibrational, electronic, thermal, and thermoelectric properties of Janus ${\mathrm{Ge}}_2\mathrm{P}X(X=\mathrm{N},\mathrm{As},\mathrm{Sb},\mathrm{and}\mathrm{Bi})$ monolayers, using first-principles calculations combined with the Landauer formalism. The suggested configurations exhibit dynamical stability and retain structural integrity even at elevated temperatures. Electronic structure calculations employing hybrid functionals (HSE06) with spin-orbit coupling reveal that ${\mathrm{Ge}}_2\mathrm{PAs}$ and ${\mathrm{Ge}}_2\mathrm{PSb}$ monolayers exhibit anisotropic characteristics as indirect semiconductors, while ${\mathrm{Ge}}_2\mathrm{PN}$ and ${\mathrm{Ge}}_2\mathrm{PBi}$ exhibit metallic behavior. We also compare the thermal, electronic, and thermoelectric transport properties of these proposed monolayers to binary 2D GeP in the ballistic limit. Notably, both ${\mathrm{Ge}}_2\mathrm{PAs}$ and ${\mathrm{Ge}}_2\mathrm{PSb}$ exhibit $n$-type figure of merit ($ZT$) values exceeding 1 at 800 K, with their $n$-type $ZT$ values surpassing that of GeP at room temperature. Our analysis underscores the distinctive structural and electronic properties of ${\mathrm{Ge}}_2\mathrm{PAs}$ and ${\mathrm{Ge}}_2\mathrm{PSb}$ monolayers, accompanied by their highly promising thermoelectric performance. These findings position them as strong candidates for energy harvesting and conversion applications.