Unveiling the Thermoelectric Properties of Group III-Nitride Biphenylene Networks

Abstract: After the synthesis of the carbon biphenylene network (C-BPN), research has increasingly focused on adapting elements from other groups of the periodic table to this lattice structure. In this study, the direction-dependent electronic, thermal, and thermoelectric (TE) properties of semiconducting group-III (group-III = B, Al, Ga, In) nitride biphenylene networks are investigated using the non-equilibrium Green's function formalism in combination with first-principles calculations. Phonon spectra and force field molecular dynamics (MD) simulations were used to asses the dynamically and thermally stable structures. At room temperature, the lowest phonon thermal conductance values are obtained for InN-BPN, with $κ{\mathrm{ph}}$ = 0.12 nW/K/nm and $κ{\mathrm{ph}}$ = 0.21 nW/K/nm along the armchair and zigzag directions, respectively. The nearly dispersionless valence-band region between the $Γ$--$X$ symmetry points causes a sharp increase in the $p$-type electronic transmission, which significantly enhances the $p$-type thermoelectric figure of merit, $zT$. Among the investigated group-III nitride BPNs, InN-BPN exhibits the best performance, with a $p$-type $zT$ value of 2.33 in the zigzag direction at 800 K.