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 sp 3 -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/Si 2 C 2 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.

First-Principles Study of AlBN and Related Polytypes

“…Hexagonality is the ratio of the number of h character to the total number of c and h characters in the unit cell. 26) In previous calculated BN (AlN) polytypes, 26,27,29,30) the total energy increases (decreases) with increasing hexagonality.…”

“…Their maximum values (Δ max ) of displacements are tabulated in Table IV, which are quite larger than those of the binary polytypes (less than 1.0 %) in the previous studies. [25][26][27][28][29][30] Therefore, it is impossible to neglect an influence of its large internal atom displacement on the tetrahedral lattice properties. In addition, a structural distortion of 2H-AlBN(Al 2 BN) is quite large although the covalent radius of B is smaller than that of N. This may induce a structural phase transition although it is not considered here.…”

“…Indices "1" in Al 2 B 1 N 1 are omitted as Al 2 BN hereafter with the exception of Table. We have investigated the electronic and lattice properties of binary BN, SiC, and AlN polytypes. [25][26][27][28][29][30] Hexagonality is an important parameter to discuss the stabilities of BN and AlN polytypes. 26) The polytype structure has cubic (c) and hexagonal (h) characters.…”