Energy state and coordination of fluorine (F)-passivated Ge surface have been theoretically analyzed by semi-empirical molecular orbital method in comparison with hydrogen-passivated Ge surface to predict usefulness of F for passivation element and surface stabilization. Heat of formation for the reaction of F atoms and Ge layer system decreased simultaneously without energy barrier. Resultantly, F-Ge bonds were formed on Ge layer system and Ge surface dangling bonds were passivated by F dissimilar to the reaction of H atoms and Ge layer system. Furthermore, it was confirmed experimentally that the electrical properties of HfO2/Ge gate stack were improved by F-2-ambient treatment of Ge substrate prior to HfO2 deposition. It is concluded that F-passivation of Ge surface is useful in making stable and low-defective Ge substrate for high-k dielectric layer deposition. (C) 2010 Elsevier B.V. All rights reserved.