Tuning electronic transport properties of in-plane-graphene–h-BN superlattices for improved thermoelectric material

In-plane graphene–h-BN (h-BN–G) superlattices have been identified as promising thermoelectric (TE) materials owing to their significantly reduced lattice thermal conductivity compared to that of pristine graphene. To further tune the TE response, variations in the superlattice period length (PL) and biaxial strain were introduced. The TE properties were evaluated using the Boltzmann transport theory within the constant relaxation time approximation, with the Wannier functions derived from density functional theory. It was revealed that the Seebeck coefficient (S) was enhanced by an order of magnitude relative to that of pristine graphene. Compared to the unstrained condition, 10% biaxial compressive strain enhances the S by ∼42%, while 10% biaxial tensile strain reduces it by ∼29%. In addition, introduction of h-BN causes the emergence of electronic bandgaps and leads to concurrent reductions in the electrical conductivity and electronic thermal conductivity per unit relaxation time near the Fermi window. Subsequently, the maximum power factor per unit relaxation time (PF/τ was enhanced by an order of magnitude relative to that of the pristine graphene near to the conduction and valence bands. With increasing PL, a narrowing of the bandgap and further reductions in PF/τ were observed. Notably, a 10% compressive strain enhances the PF/τ for both carrier types, while a 10% tensile strain suppresses it. Furthermore, the response to strain is highly asymmetric between the electrons and holes. These findings demonstrate that band engineering through control of grown PL and applied strain offers an effective approach for tuning the electronic transport properties of the h-BN–G TE applications.