Doping in cubic silicon-carbide

We studied the energetics and the properties of impurity states that result from doping cubic silicon-carbide (3C-SiC) with aluminum (Al), boron (B), and nitrogen (N) atoms using the tight-binding linear combination of muffin-tin orbital atomic sphere approximation method. For Al doping, it is only favorable to substitute Al for Si atoms. The corresponding hole states contribute to a partially filled weak peak near the Fermi energy. For B doping, it is possible to replace either Si or C atoms in the crystal. When a B atom is at a Si site, the hole states exhibit behavior similar to the case of Al doping. However, when a B atom is at a C site, the hole states form a partially filled strong peak above the Fermi energy. This localized feature is explained in terms of the screening effect of the neighboring atoms. For n-type doping, a N atom can enter either the Si or C site. The latter site is more energetically favorable. Furthermore, the corresponding donor states form deep impurity states within the gap. In contrast, when a N atom is at a Si site, shallow donor states are formed. (C) 1999 American Institute of Physics. [S0003-6951(99)01027-X].