Microstructural Evolution and Electrical Characteristics of Co-Germanide Contacts on Ge

Abstract

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...

Structural and Magnetic Properties of CoGen− (n=2–11) Clusters: Photoelectron Spectroscopy and Density Functional Calculations

“…[4,5,30] It has been reported that cobalt-doped germanium nanomaterials have low resistivity, high thermal stability, and room temperature ferromagnetism; this results in potential applications in effective on-chip interconnects and nanoelectrodes for highly integrated nanoelectronic devices, spintronic devices, and field-emission displays. [31][32][33][34][35][36] Investigating the structural and electronic properties of cobalt-doped germanium clusters may provide valuable information for developing cobalt/germanium materials, as well as their applications in electronic and magnetic materials. There have been several experimental and theoretical studies on cobalt-doped germanium clusters.…”

The Electronic Structures of CoGen–/0 (n = 1–3) Clusters from Multiconfigurational CASSCF/CASPT2 and RASSCF/RASPT2 Calculations

“…In this configuration, 19a 1 , 20a 1 , 8b 1 , 14b 2 , and 5a 2 are predominantly 3d of Co, while 17a 1 , 18a 1 , and 7b 1 are mainly 4p orbitals of Ge 2 ligands. 3 A 1 and 3 A 2 are formed from 3 B 1 by moving one electron from 19a 1 and from 5a 2 to the 8b 1 orbital. At the RASPT2 level, 3 A 1 and 3 A 2 are computed to be just 0.06 and 0.15 eV above the ground state.…”

“…Cobalt-doped germanium clusters have attracted great attention of scientists because of their potential applications in electronic and magnetic materials. − Investigation on the geometrical and electronic structures of cobalt-doped germanium clusters was performed with several experimental and theoretical methods. ,− Regarding the CoGe n –/0 ( n = 1–3) clusters, the structural, electronic, and magnetic properties of the neutral clusters were studied with density functional theory, but the spin states of these clusters were not reported. , Also, the photoelectron spectra of CoGe 2 – and CoGe 3 – clusters were measured with a photon energy of 266 nm . The anion spectra showed four bands at 1.96, 2.71, 3.33, and 3.60 eV for CoGe 2 – and four bands at 2.12, 2.66, 3.37, and 3.98 eV for the CoGe 3 – cluster.…”

Effect of Thermal Annealing Temperatures on MSM Photo Detector Based on Ge-like Micro Flowers in the Dark Mode

“…The fundamental purpose of any photodetector is to convert optical signals into electrical signals, usually expressed as a photocurrent, which can be amplified, displayed and/or retransmitted. Ge has been attractive as an alternative substrate to Si because Ge has higher carrier mobility over Si and good compatibility with Si processing [3]. Due to its optical properties, Ge is a good candidate for the development of light detectors operating in the near infrared region (NIR: 800-1600 nm) especially when integration with Sibased devices are required.…”