Remarkable Band-Gap Renormalization via Dimensionality of the Layered Material C3B

Layer-dependent electronic and structural properties of emerging graphitic carbon-boron compound C3B are investigated using both density-functional theory and the GW approximation. We discover that, in contrast to a moderate quasiparticle band gap of 2.55 eV for monolayer C3B, the calculated quasipar-ticle band gap of perfectly stacked bulk phase C3B is as small as 0.17 eV. Therefore, our results suggest that layered material C3B exhibits a remarkably large band-gap renormalization of over 2.3 eV due to the interlayer coupling and screening effects, providing a single material with an extraordinary band-gap tunability. The quasiparticle band gap of monolayer C3B is also over 1.0 eV larger than that of C3N, a closely related two-dimensional semiconductor. Detailed inspections of the near-edge electronic states reveal that the conduction-and valence-band edges of C3B are formed by out-of-plane and in-plane elec-tronic states, respectively, suggesting an interesting possibility of tuning the band edges of such layered material separately by modulating the in-plane and out-of-plane interactions.