C 3 N based heterobilayers: a potential platform to explore optoelectronic and thermoelectric properties

We theoretically investigate the full thermal transport and optoelectronic features of two estab- lished van der Waals (vdW) heterostructures based on the recently synthesized monolayer of C 3 N using the machinery of the Boltzmann transport and GW+BSE calculations. Among the structures, C 3 N/hBN tends to exhibit a small indirect gap semiconducting nature with an admixture of com- paratively higher 'flat-and-dispersiveness' and band degeneracy in the conduction band minima. A nearly comparable high thermoelectric power factor is observed for both the charge carriers at 300 K and 900 K at specific concentrations. The other material, C 3 N/graphene however maintains a low Seebeck coefficient with large electrical conductivity which correctly manifests its metallic character. A combination of low atomic mass, higher anharmonicity and longer lifetime of acous- tic phonons in C 3 N/hBN results in an intermediate lattice thermal conductivity (196 Wm -1 K -1 ) at room temperature as compared to its constituent monolayers. Under heavy n-type doping, C 3 N/hBN hetero-bilayer displays a figure of merit value of 0.13 (and 0.36) at room temperature (and at 900 K). As per the optical signatures are concerned, C 3 N/hBN reveals two distinct absorp- tion peaks with a high electron-hole quasiparticle interaction energy correction. Besides both the structures display a much better absorption throughout the spectrum compared to graphene. We expect these findings will motivate future research in designing thermoelectric and optoelectronic materials made of light mass, earth-abundant and non-toxic elements.