Ge is a promising starting material for device fabrication due to its advantages, which include narrow band gap, high hole mobility, and high solubility for p-type dopants [1,2]. In order to clean the Ge surface prior to gate oxidation, surface oxidation, and etching must occur in succession. Because the formation of a gate oxide layer on the atomically smooth surface is crucial to improve the performance of devices, oxidation chemistry on the Ge surface needs to be understood. However, the surface oxidation mechanism of Ge is not firmly established in comparison to that of Si. Although it has been theoretically studied that, after the first insertion of one oxygen molecule into the Ge backbond, thermal activation in the dry oxidation allows the oxygen bridging the dimmer site to be inserted into the second Ge backbond in the same dimmer [3], the oxidation mechanism of the Ge surface in a wet chemical solution needs to be studied further.
It is reported that Ge oxide is formed in acid solutions, such as H 2 O 2 and HNO 3 solutions [4], but through these means a growth of thick oxide and formation of large oxide nuclei can also occur [5], making the Ge surface atomically rough. Methanol (MeOH) has been widely used to clean the Ge surface [6,7]. However, the behavior of the Ge surface in a MeOH solution has not been extensively elucidated. Lim et al. reported that vaporized MeOH is dissociated into methyl radical and hydroxyl species, and a methoxy-incorporated Ge-O-Ge structure was formed on the clean Ge(1 0 0) surface prepared by a repetition of Ar sputtering and annealing at 600 8C [8]. Bae et al. reported that adsorption of MeOH vapor on a clean Ge surface formed H-Ge-Ge-OCH 3 through a kinetically favorable O-H bond dissociation [9]. However, in the device fabrication process, the semiconductor surface is often cleaned by HF solution to remove residual oxides, producing H-termination on the surface. The surface chemistry of a Ge surface may be different depending on the surface termination, and the behavior of termination and oxidation on the surface may change in the liquid solution. In this study, the behavior of liquid MeOH on a Ge(1 0 0) surface is systematically examined. In particular, the characteristics of a Ge surface in the presence of iodine (I 2 ) in MeOH are investigated, which will improve understanding of the termination and oxidation mechanism to achieve a smooth and robust Ge surface.
An attenuated total reflection (ATR) crystal was prepared using an undoped Ge(1 0 0) wafer (resistivity >40 V cm) for multiple internal reflection Fourier transform infrared spectro-