First-Principles Study of Various BN, SiC, and AlN Polytypes

Abstract

We have investigated the electronic and lattice properties of 48H-BN, 20H-SiC, and 30H-AlN polytypes which are sp³-bonded compounds. Their electronic and lattice properties were calculated using the total energy pseudopotential method based on the local density approximation (LDA). As for AlN polytypes (2H, 3C, 4H, 6H, 10H), we investigated using the total energy pseudopotential method based on the generalized gradient approximation (GGA) for comparison with the LDA results. 48H-BN has huge number of possible polytype structures and we chose one polytype structure as “24.24” (Zhdanov notation). “24.24” is not “2424”, which means twenty-four “+” and twenty-four “-” symbols in the Hägg notation. We treat three polytype structures of 20H-SiC as “33322322”, “33332222”, and “32322323” (Zhdanov notations). Their total energies are slightly higher by 0.22 meV/Si₂C₂ than that of 4H-SiC. Although all the AlN polytypes calculated by LDA have indirect band gaps with the exception of 2H-AlN, 10H-AlN(212212) calculated by GGA has a direct band gap. Its hexagonality is 60 % and “212212” is the Zhdanov notation.