Adsorption of N-containing species onto SiC(0001) surfaces: A theoretical study

Abstract

Adsorption of nitrogen-containing species onto the Si and C surfaces of SiC(0001) has been theoretically investigated, using density functional theory calculations under periodic boundary conditions. The idea was then to investigate nitrogen incorporation during in situ doping of SiC. As a guide to the composition of gaseous species above a growing SiC surface, earlier results from thermodynamic calculations, performed at experimental conditions for N in situ doping, were used. The present results show that adsorption of ${\mathrm{N}}_{2},$ N, ${\mathrm{NH}}_{3},$ ${\mathrm{NH}}_{2},$ CN, HCN, HNC, ${\mathrm{H}}_{2}\mathrm{CNH},$ SiN, SiNH, and ${\mathrm{Si}}_{2}\mathrm{N},$ with three exceptions, is exothermic to both SiC surfaces. The exceptions include adsorption of ${\mathrm{NH}}_{3}$ or the N atom in HCN or HNC to the C surface. The twofold adsorption processes were all found to be exothermic and more favorable for the Si than for the C surface. Furthermore, adsorption by the N(Si) atom in the adsorbate was found to be stronger to the Si(C) surface while the adsorbates seem to bind equally strongly to both surfaces by the C atom. There was generally a clear correlation between larger adsorption energies, shorter bond lengths and higher bond overlap populations in the region between the bonding atoms.