The microstructural evolution and corresponding electrical contact properties of Co-germanide systems were investigated. The Co-germanide formation process underwent several intermediate, high-resistive phases ͑CoGe and Co 5 Ge 7 ͒, while low-resistive CoGe 2 was formed over 650°C in a narrow process window of Ͻ100°C. Because of the strong Fermi level pinning effect, Co, CoGe, and Co 5 Ge 7 phases exhibited Schottky contact behaviors with similar Schottky barrier heights on n-type Ge and ohmic contact behavior on p-type Ge, respectively. However, for the CoGe 2 /n-type Ge contact formed at 700°C, a nearly ohmic contact behavior started to appear, which was attributed to the possible diffusion of Co atoms into the Ge substrate due to the hightemperature germanidation process.Recently, a variety of alternative channel materials having a high intrinsic carrier mobility, such as Ge and compound semiconductors, has been widely studied due to their potential to allow the speed of transistors to reach a level that is unattainable with the conventional Si substrate and to assist in the ongoing miniaturization of the devices. 1,2 Furthermore, the lack of stable grown-oxides of Ge and compound substrates has been overcome by the recent progressive development of the deposited high-k gate dielectrics that have replaced SiO 2 in metal oxide semiconductor field-effect transistor ͑MOSFET͒ devices, such as ZrO 2 , HfO 2 , and Hf-silicates. Although many process problems remain to be resolved, some devices fabricated based on high-k and alternative channel materials have demonstrated very promising electrical results. 2,3 With its high carrier mobility and excellent process compatibility with the current Si processing ͑compared to compound semiconductor͒, Ge is a very attractive possible candidate for the Si replacement.In Si-based MOSFETs, various metal silicides have been widely used as a contact material due to their low resistance, low-formation temperature, and good thermal stability to reduce the contact and parasitic resistance in source and drain regions. 4 Similarly, metal germanide appears as a natural candidate for Ge-based devices. The successful development of metal germanide as a contact material requires understanding the exact phase/microstructural evolution occurring during annealing of metal films on Ge and the corresponding electrical contact properties with p-or n-doped Ge substrates. Among many possible metal-germanide systems, the successful application of Ni-and Co-silicides in the Si-based technology has led researchers to target their corresponding germanides as promising candidates for contact materials in Ge-based devices.The phase evolution of Ni-and Co-germanides as a function of the formation temperatures has been carefully studied by many researchers, 5-8 and their Schottky diode properties were also reported. 5,9-12 However, only a few studies have focused on the Co/Ge system, 7,8,11 while the electrical contact properties on substrates with different doping types and various germanide phases rema...

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