Investigating the CVD Synthesis of Graphene on Ge(100): toward Layer-by-Layer Growth

Abstract

Germanium is emerging as the substrate of choice for the growth of graphene in CMOS-compatible processes. For future application in next generation devices the accurate control over the properties of high-quality graphene synthesized on Ge surfaces, such as number of layers and domain size, is of paramount importance. Here we investigate the role of the process gas flows on the CVD growth of graphene on Ge(100). The quality and morphology of the deposited material is assessed by using μ-Raman spectroscopy, X-ray photoemission spectroscopy, scanning electron microscopy, and atomic force microscopy. We find that by simply varying the carbon precursor flow different growth regimes yielding to graphene nanoribbons, graphene monolayer, and graphene multilayer are established. We identify the growth conditions yielding to a layer-by-layer growth regime and report on the achievement of homogeneous monolayer graphene with an average intensity ratio of 2D and G bands in the Raman map larger than 3.

Driving with temperature the synthesis of graphene on Ge(110)

“…Finally, we suggest that the nucleation of embryos graphene bilayer observed at TD= 930 ° is also in line with the formation of a quasi-liquid Ge surface layer which boosts the mobility of Ge atoms and their diffusional flow up to the surface of the first graphene layer, in line with what was observed on Ge(001) [13,20].…”

“…Alternative synthetic approaches, such as the unzipping of carbon nanotubes typically used for obtaining sub-10 nm graphene nanoribbons and flakes [6][7][8], suffer from the same issue, due to contamination by metal nanoparticles originating from the growth process of nanotubes. Thanks to the catalytic activity of Ge on gaseous carbon precursors combined with Ge carbides instability, chemical vapor deposition (CVD) of graphene on Ge or Ge/Si substrates represents a viable growth route [9][10][11][12][13][14][15] for obtaining metal-free, CMOS-compatible graphene. After the seminal works by Wang et al [9] and Lee et al [10] on Ge(110), most of the attention has been focused on the Ge(001) surface, this being, in principle, the most technologically relevant one.…”

Abrupt changes in the graphene on Ge(001) system at the onset of surface melting

“…Temperatures 5° C higher than 930 °C resulted in poorer graphene quality and a partial melting of the Ge substrate. Using the CVD parameters described above, at TD= 930 °C and for a deposition time tD= 60 min, we obtained a state-of-the-art single-layer graphene, grown in a layer-by-layer mode, which we will take as a reference sample [14]. Here we performed an accurate and fine reduction of the growth temperature to highlight its impact on the growth process.…”

Direct CVD Growth of Graphene on Technologically Important Dielectric and Semiconducting Substrates

“…After this, Scaparro et al attempted the direct CVD growth of graphene on Ge(100) substrates by varying the H 2 /CH 4 flow ratio, and the growth time in order to understand the growth mechanism and morphology 126. Graphene samples were grown in a commercially available 4 inch cold‐wall LPCVD reactor with 200 and 800 sccm flow rates of H 2 and Ar, respectively, whereas the CH 4 flow rate varied between 1 and 10 sccm.…”