Chemical reactivity of. uorine molecule (F-2)-germanium (Ge) surface and dissociation of. uorine (F)-Ge bonding have been simulated by semi-empirical molecular orbital method theoretically, which shows that F on Ge surface is more stable compared to hydrogen. Ge MIS (metal insulator semiconductor) capacitor has been fabricated by using F-2-treated Ge(1 0 0) substrate and HfO2 film deposited by photo-assisted MOCVD. Interface state density observed as a hump in the C-V curve of HfO2/Ge gate stack and its C-V hysteresis were decreased by F-2-treatment of Ge surface. XPS (X-ray photoelectron spectroscopy) depth pro. ling reveals that interfacial layer between HfO2 and Ge is sub-oxide layer (GeOx or HfGeOx), which is believed to be origin of interface state density. F was incorporated into interfacial layer easily by using F-2-treated Ge substrate. These results suggest that interface defect of HfO2/Ge gate stack structure could be passivated by F effectively. (C) 2008 Elsevier B. V. All rights reserved.