Interstitial Channels that Control Band Gaps and Effective Masses in   Tetrahedrally Bonded Semiconductors
  We find that electron states at the bottom of the conduction bands of covalent semiconductors are distributed mainly in the interstitial channels and that this floating nature leads to the band-gap variation and the anisotropic effective masses in various polytypes of SiC. We find that the channel length, rather than the hexagonality prevailed in the past, is the decisive factor for the band-gap variation in the polytypes. We also find that the floating nature causes two-dimensional electron and hole systems at the interface of different SiC polytypes and even one-dimensional channels near the inclined SiC surface. 
Yu-ichiro Matsushita, Atsushi Oshiyama
cond-mat.mtrl-sci