Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures

© 2016 Author(s). Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications

Quasi free-standing epitaxial graphene fabrication on 3C-SiC/Si(111)

© 2018 IOP Publishing Ltd. Growing graphene on SiC thin films on Si is a cheaper alternative to the growth on bulk SiC, and for this reason it has been recently intensively investigated. Here we study the effect of hydrogen intercalation on epitaxial graphene obtained by high temperature annealing on 3C-SiC/Si(111) in ultra-high vacuum. By using a combination of core-level photoelectron spectroscopy, low energy electron diffraction, and near-edge x-ray absorption fine structure (NEXAFS) we find that hydrogen saturates the Si atoms at the topmost layer of the substrate, leading to free-standing graphene on 3C-SiC/Si(111). The intercalated hydrogen fully desorbs after heating the sample at 850 °C and the buffer layer appears again, similar to what has been reported for bulk SiC. However, the NEXAFS analysis sheds new light on the effect of hydrogen intercalation, showing an improvement of graphene's flatness after annealing in atomic H at 600 °C. These results provide new insight into free-standing graphene fabrication on SiC/Si thin films

A thin film approach for SiC-derived graphene as an on-chip electrode for supercapacitors

© 2015 IOP Publishing Ltd. We designed a nickel-assisted process to obtain graphene with sheet resistance as low as 80 Ω square-1 from silicon carbide films on Si wafers with highly enhanced surface area. The silicon carbide film acts as both a template and source of graphitic carbon, while, simultaneously, the nickel induces porosity on the surface of the film by forming silicides during the annealing process which are subsequently removed. As stand-alone electrodes in supercapacitors, these transfer-free graphene-on-chip samples show a typical double-layer supercapacitive behaviour with gravimetric capacitance of up to 65 F g-1. This work is the first attempt to produce graphene with high surface area from silicon carbide thin films for energy storage at the wafer-level and may open numerous opportunities for on-chip integrated energy storage applications

On-silicon supercapacitors with enhanced storage performance

© 2017 The Electrochemical Society. All rights reserved. The expanding development of portable electronic devices and ubiquitous sensing systems has created a strong demand for efficient miniaturized energy storage units, with planar geometries and capable of being integrated on a silicon platform. Generally, the performance of thin-film storage devices, including using graphene, is dramatically limited by their low surface area for ionexchange. We had recently shown that a higher number of graphene layers does not translate into higher storage performance. Here we show a way to overcome this limitation and achieve a maximum accessible area for ion exchange. A repeated graphitization strategy using a nickel catalyst on epitaxial silicon carbide films on silicon yields few-layers graphenic nanocarbon electrodes with prominent edge defects, facilitating the intercalation between multiple graphenic sheets while maintaining overall a high electrode conductivity

Electron effective attenuation length in epitaxial graphene on SiC

© 2018 IOP Publishing Ltd. The inelastic mean free path (IMFP) for carbon-based materials is notoriously challenging to model, and moving from bulk materials to 2D materials may exacerbate this problem, making the accurate measurements of IMFP in 2D carbon materials critical. The overlayer-film method is a common experimental method to estimate IMFP by measuring electron effective attenuation length (EAL). This estimation relies on an assumption that elastic scattering effects are negligible. We report here an experimental measurement of electron EAL in epitaxial graphene on SiC using photoelectron spectroscopy over an electron kinetic energy range of 50-1150 eV. We find a significant effect of the interface between the 2D carbon material and the substrate, indicating that the attenuation length in the so-called 'buffer layer' is smaller than for free-standing graphene. Our results also suggest that the existing models for estimating IMFPs may not adequately capture the physics of electron interactions in 2D materials

Solid source growth of graphene with Ni-Cu catalysts: Towards high quality in situ graphene on silicon

© 2017 IOP Publishing Ltd. We obtain a monolayer graphene on epitaxial silicon carbide on silicon substrates via solid source growth mediated by a thin Ni-Cu alloy. Raman spectroscopy consistently shows an ID/IG band ratio as low as ∼0.2, indicating that the graphene obtained through this method is to-date the best quality monolayer grown on epitaxial silicon carbide films on silicon. We describe the key steps behind the graphene synthesis on the basis of extensive physical, chemical and morphological analyses. We conclude that (1) the oxidation, amorphisation and silicidation of the silicon carbide surface mediated by the Ni, (2) the liquid-phase epitaxial growth of graphene as well as (3) the self-limiting graphitization provided the molten Cu catalyst, are key characteristics of this novel synthesis method

A graphene platform on silicon for the Internet of Everything

© 2018 IEEE. We have pioneered a platform technology able to harness the properties of graphene directly from silicon carbide on silicon substrates for integrated on-chip or in-package applications, ranging from sensing and nanophotonics to integrated energy storage. The graphene synthesis is transfer-free and site-selective, leading to straightforward wafer-level fabrication and yielding sufficient adhesion for subsequent processing. This approach among others can pave the way towards miniaturized energy sources in SiP systems for smart nodes of the Internet of Everything