The relations between physical structural transformations and improvement of electrical properties of metal/GeO2/Ge systems using low temperature oxidation and the post metal deposition annealing (PDA) have been investigated. In metal/GeO2/Ge systems, we found that the electrical properties were drastically improved by the oxidation and the PDA. The oxidation at low temperature achieves no C-V hysteresis because of suppression of GeO desorption. on the other hand, according to results of X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS), the improvement mechanism of electrical properties of metal/GeO2/Ge structures after the PDA was clearly shown as follows. Once the metals were deposited on the GeO2, GeOx layer was formed at the surface region of the GeO2 due to reduction of the oxide by the metals. The sub-oxide layer at the interface causes a large negative flat-band voltage (V-FB) shift on the capacitance-voltage (C-V) characteristics of the metal/GeO2/Ge structures. Then, during the PDA process at low temperature, the sub-oxide layer is disappeared with desorbing as germanium monoxide (GeO) gas, and the VFB shifts of the metal/GeO2/Ge systems were drastically improved and also their accumulation capacitances were increased because of disappearance of the sub-oxide layer. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3581033] All rights reserved.