Density functional theory is employed to investigate atomic layer deposition mechanism of HfO2, on Ge(I 0 0)-2 x I surface. Both the HfCl4 and H2O half-reactions proceed through an analogous trapping-mediated mechanism. The neighboring hydroxyl in the reaction of HfCl4 with two Ge-OH* sites has a major effect on the formation of HfCl4 adsorbed complex. In addition, both the Ge and Si reaction pathways are qualitatively similar, however, adsorption of HfCl4 is favorable on Ge than on Si surface hydroxyl sites. By comparison of the reactions of H2O on the different surfaces, the differences in energy are negligible to alter the reaction mechanism.