Electronic structure of (diamond C)/(sphalerite BN) (110) interfaces and superlattices

An electronic-structure study of the (diamond C)/(sphalerite BN) (110) interface using the linear-muffin-tin-orbital and local-density-functional methods is presented. The energy of formation of superlattices ${\mathrm{C}}_{2\mathrm{n}}$(BN${)}_{\mathrm{n}}$ for n=1,3,5 were calculated to be 0.89, 0.95, and 0.94±0.01 eV/(interface unit-cell area), the positive values indicating thermodynamic instability of these superlattices towards disproportionation. Comparison of these interfacial energies to estimates of the surface cleavage energies [of the order of 5 eV/(surface unit-cell area)] based on a bond-breaking argument shows that strong bonding, only ∼10% weaker than the bonding in the bulk solids, is occurring at the interface. The valence-band offset is calculated by means of the previously developed ‘‘self-consistent dipole-profile approach’’ using superlattices of five, seven, and nine layers of each material and is found to be 1.45 eV. Using the fully-self-consistent atomic-sphere-approximation potential of the central layers of the 5+5 superlattice yields a value of 1.41 eV. Both are in very good agreement with a recent calculation by Pickett [Phys. Rev. B 38, 1316 (1988)], who obtained 1.42±0.04 eV. Using the experimental band gaps, this leads to the less common type-II alignment with a conduction-band offset of 0.5 eV. The calculated minimum band gaps of the bulk semiconductors including an approximate quasiparticle self-energy correction are shown to be in good agreement with the experimental gaps. Details of the charge distribution, local densities of states, and superlattice band structures are presented and discussed. They show that the interface region extends essentially over two layers in each solid. The layer charge distribution leading to the interface dipole shows pronounced oscillations.