We systematically investigate adsorption behavior of Al and N atoms on 4H-SiC (1 1 (2) over bar 0) surfaces based on first-principles calculations. The calculations for stable adsorption site demonstrate that the Al atom is adsorbed at the lattice site of 4H structure whereas the N atom is incorporated at the interstitial site. The calculated surface phase diagrams for Al and N atoms as functions of beam equivalent pressure and temperature clarify that Al atoms can be adsorbed at all of the adsorption sites below 1800 K and N atoms, in contrast, are desorbed excepting the most stable site above 1150 K. These temperatures imply that under experimental conditions (1223 K) Al atoms can be easily adsorbed and N atoms are adsorbed only on the most stable adsorption site. Furthermore, the calculated barrier heights of adsorbed Al and N atoms are 1.0 and 1.8 eV, respectively, implying that the surface migration of Al atoms is prominent compared to that of N atoms. These results obtained thus manifest that adsorption behavior of Al and N atoms is quite different and the growth processes change depending on V/III ratio under molecular beam epitaxy growth. (C) 2009 Elsevier B. V. All rights reserved.