Nitrogen (N) is one of the most interesting n-type dopant for wide band-gap semiconductors (diamond, silicon carbide) due to its low mass and to the easy way with which it can be chemically manipulated.
In device processing it is often interesting to achieve very high doping doses of the substrate and N has proven not to be the best choice, as its activation rate starts decreasing when a certain threshold in the dose is reached. Particularly, in silicon carbide has been shown that for doses of the order of 1020 cm-3 it is more convenient to implant phosphorus or, to a lesser extent, to co-implant nitrogen and phosphorus.
In this work we present a first-principles theoretical study of the most relevant mechanisms that lead to N clusters passivation in silicon carbide (SiC) to account for N poor activation rate. We will shown that all the N complexes, dominant in the different doping condition of the host material, do self-passivate, although the mechanism is not always the same. The role of the off-centre relaxation of substitutional N at a Si site is also discussed.