First-Principles Calculations of Impurity States in 3C-SiC

The electronic structures, atomic geometries, and formation energies of several substitutional impurities in 3C-SiC are calculated by the first-principles pseudopotential method. N is considered as the n-type dopant and Al and B as the p-type dopants. It is shown that N forms a shallow donor level on a C site and a localized state on a Si site, and both Al and B form a shallow acceptor level on a Si site and a deep level on a C site. For N, a C site has the lower formation energy than a Si site. For Al, a Si site has the lower formation energy than a C site. These features do not depend on the composition. For Al and N, the impurities on the favorable sites form shallow levels while for B, the lower formation energy site depends on the composition. A C site is favorable for B under Si-rich conditions and a Si site under C-rich conditions. These results suggest that the low-resistivity p-type SiC crystal can be fabricated under C-rich conditions when B is employed as a dopant.