On the impact of nitrogen and aluminum doping on silicon carbide polytype stability: Insights from first principle calculations

Silicon carbide (SiC) can form many different polytypes but their energetic ordering and frequency of occurrence are still not fully understood. In this study, polytype stability in pure and doped SiC as well as charged defects are studied by first-principle calculations. The dopants under investigation include N and Al which are added as single dopants and also as dopant pairs. Regarding pure SiC, our findings align with previous works which have shown that energy differences between polytypes are smaller than uncertainties related to the choice of exchange-correlation functional. In contrast, the effects of doping are predicted consistently for different xc functionals with N doping leading to a stabilization of the 3C polytype while Al doping causes only minor changes. This effect is explained based on the differences in the band-gap of the polytypes and the dopant-induced defect states in agreement with an explanation suggested by Heine et al (J Am Ceram Soc. 1991;74(10):263033). We further corroborate this explanation with calculations of charged dopants. As a consequence, Al in proximity to N can entirely neutralize the donor and its stabilization effect on 3C. Furthermore, a strong attraction (1.8–1.9 eVs) is observed between the two dopants which indicates that they will occur in pairs. Our results provide a more complete picture of SiC doping and we discuss its implications for the crystal growth process.