The authors investigated the surface passivation mechanisms of H-terminated Ge(100)(2 x 1) by atomic layer deposition of Al2O3, AlN through first-principles calculation method. The formation of initial Al2O3 and AlN passivation layer on Ge surface is investigated at atomic scale and the corresponding reaction pathways for both the reaction are also presented. The reaction barrier heights of H2O and NH3 half reaction are 0.53 eV/mol and 0.51 eV/mol higher than that of Al(CH3)(3) half reaction, respectively which indicates that the overall passivation processes of the both reactions are limited by the second half reaction. Moreover, the chemisorption state and product state of the NH3 half reaction are found to be in the same energy level, and it is possible that the second half reaction of AlN will be trapped in a chemisorption state. (C) 2011 Elsevier B.V. All rights reserved.