J. Phys. Soc. Jpn. 81, 024714 (2012) [13 Pages]

First-Principles Study of 8H-, 10H-, 12H-, and 18H-SiC Polytypes

+ Affiliations
1National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan

We calculated the electronic and lattice properties of 8H-, 10H-, 12H-, and 18H-SiC polytypes, which are sp 3 -bonded compounds. A tetrahedral structure is formed by Si and C atoms in their hexagonal polytypes. Their possible symmetries are P 6 3 m c and P 3 m 1. All possible structures in the 8H polytype, six structures in the 10H polytype, seven structures in the 12H polytype, and one structure in the 18H polytype were considered. The calculated hexagonalities ( H ) are 16.7, 20, 25, 33.3, 40, 44.4, 50, 60, 66.7, 75, 80, and 83.3%. Hexagonality is a ratio of the number of hexagonal ( h ) characters and total number of cubic ( c ) and h characters in a unit cell. We calculated their electronic properties [i.e., electronic band structures, band gaps, valence band maximum (VBM), and conduction band minimum (CBM)]. All the calculated electronic band structures are nonmetallic and the band gaps are indirect. The lattice properties (i.e., lattice constants and internal coordinates of atoms in the unit cell) were optimized by the total energy pseudopotential method based on the local density approximation (LDA). There is no clear trend in the order of the total energies for the SiC polytype structures. The total energies of three 10H-SiC polytype structures are slightly lower than that of 4H-SiC. One of them, whose stacking sequence is ABCACBCACB (ABC notation) and whose H = 40%, is lower by 2.4 meV/Si 2 C 2 than 4H-SiC, and lowest in the SiC polytype structures calculated by LDA. The Zhdanov notation of 10H-SiC(ABCACBCACB) is “3322”. As for the 2H-, 3C-, 4H-, 6H-, 8H-, and 10H-SiC polytypes, we obtained their electronic and lattice properties using the total energy pseudopotential method based on the generalized gradient approximation (GGA) for comparison with the LDA results.

©2012 The Physical Society of Japan