B. Lutzer, M. Hummer, S. Simsek, C. Zimmermann, A. Amsuess, H. Hutter, H. Detz, M. Stöger-Pollach, O. Bethge, E. Bertagnolli:
"Rhodium Germanide Schottky Barrier Contacts";
ECS Journal Of Solid State Science And Technology, 4 (2015), 9; S. P387 - P392.

Kurzfassung englisch:
Rhodium Schottky barrier contacts on germanium substrates are investigated in terms of electrical, physical, and chemical properties. The Rh, deposited by electron beam evaporation on a n-type (100)-Ge substrate, has been annealed in N2H2 at different temperatures ranging from 450°C up to 800°C. Rh/Ge Schottky diodes were fabricated to extract the Schottky barrier height, the ideality factor as well as the forward to backward current ratio. By using various analyzing techniques such as Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), and High-resolution Transmission Electron Microscopy (HR-TEM), the formation of polycrystalline Rh-germanide RhxGey phases has been proven. At 500°C germanidation temperature an effective SBH of 0.59 eV is extracted showing a high current ratio of 5 × 103 and a remarkable low ideality factor of 1.07.

Germanium channel MOSFETs are currently undergoing a phase of intensive scientific research due to the high hole and electron mobilities of germanium compared to the well-established semiconductor material Si.1 However, the formation of low resistance Schottky contacts to Ge is still challenging. A subset of those contacts are the so-called germanides, binary compounds consisting of a metal and germanium, similar to the well-known and widely used silicides which are compounds involving silicon.2-6

Out of all possible germanides Ni/Ge7-9 and Pt/Ge9-12 have already gained wide attention in research. Three other combinations of platinum group metals, namely Ir/Ge, Pd/Ge and Ru/Ge have been already investigated by A. Chawanda, et al.13-15

A material combination not yet examined for the use as Schottky contact is rhodium-germanide (Rh-Ge). Only few reports exist on RhxGey compounds, like phase diagrams by Zhuravlev et al.,16 crystallographic studies by M. Wittmer et al.17 and X-ray Diffraction/resistivity measurements on Ge(001) by S. Gaudet et al.18 Contrary to rhodium germanide, the Rh-Si silicide has already undergone investigation by different means.19-23

Next to a high workfunction of 4.98 eV24 making rhodium to an interesting candidate for pMOS devices, a main advantage of rhodium is its lower intrinsic resistivity of 4.5 × 10−8 Ω·m compared to 1.0 × 10−7 Ω·m of platinum.24 Additionally, rhodium shows an even higher chemical resistance then platinum against several acids.25 Therefore Rh-Ge contacts can be considered as a worthwhile subject for use in for example next generation ultrascaled Ge-based Schottky-barrier MOSFET devices.
In this work Rh-Schottky barrier contacts on n-type (100)-Ge substrates undergoing thermal treatments in N2H2 in a temperature range of 450°C to 800°C are investigated by using Schottky diodes. Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), and High-resolution Transmission Electron Microscopy (HR-TEM) have been used to provide in-depth structural and electrical analyses of the formed RhxGey.

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