Direct Synthesis of Armchair Graphene Nanoribbons on Ge(001)/Si(001) Using CVD
Authors: Saraswat Vivek , Yamamoto Yuji , Jacobberger Robert M , Way Austin J , Arnold Michael S 
Published: February 2020

Direct synthesis of graphene nanoribbons on dielectric or semiconducting substrates offers a scalable route for integration of graphene-based devices into a conventional silicon-based technology.(1) So-far, wafer-scale synthesis of armchair graphene nanoribbons has been demonstrated on Ge (001) using chemical vapor deposition.(2) However, direct synthesis of graphene or graphene nanoribbons has not yet been achieved on CMOS compatible Si(001) due to formation of stable SiC at temperatures > 1000 K, which are needed to achieve synthesis of nanoribbons with smooth, armchair edges. A promising and realistic way to overcome this challenge is to synthesize graphene nanoribbons on CMOS compatible Ge(001)/Si(001) substrates.
So far the synthesis of monolayer graphene on Ge(001)/Si(001) substrates has been demonstrated by CVD.(3, 4) In this study, we synthesized graphene nanoribbons on 3 µm epitaxial Ge(001)/Si(001) substrates, by ambient pressure CVD using methane as the carbon precursor. We show that growth kinetics of graphene nanoribbons on Ge(001)/Si(001) are comparable to that on Ge(001). By tuning the methane flow and growth time we are able to synthesize graphene nanoribbons ranging from 100 nm to 1 µm in length with high aspect ratios, whilst avoiding Si diffusion from the bulk. For instance, by restricting methane to < 6000 ppm and growth time to < 3h, graphene nanoribbons with widths < 10 nm can be synthesized with aspect ratios as high as 70. Such nanoribbons grown on Ge(001) have been shown to exhibit technologically relevant band-gaps as well as exceptional charge transport properties.(5)
Furthermore, we also investigated the possible role of threading dislocations in Ge epilayer on nucleation or growth of nanoribbons and show that nanoribbons readily grow over the threading dislocations. Lastly, we studied the evolution of surface roughness with the nucleation density of nanoribbons. Our study provides valuable insight into the mechanism of graphene nanoribbon growth on Ge(001)/Si(001) substrates. From this information, it is expected that unidirectional graphene nanoribbons with rational placement and control over width poly-dispersity can be synthesized on Ge(001)/Si(001) platform akin to Ge(001), which has been demonstrated recently using seed-mediated growth.(6) This provides a scalable way for wafer scale integration of graphene nanoribbon arrays on Si and provides motivation for further research into this direction.

References

A. Khan et al., Direct CVD Growth of Graphene on Technologically Important Dielectric and Semiconducting Substrates. Advanced Science
5, (2018).

R. M. Jacobberger et al., Direct oriented growth of armchair graphene nanoribbons on germanium. Nature Communications
6, (2015).

I. Pasternak et al., Graphene growth on Ge(100)/Si(100) substrates by CVD method. Scientific Reports
6, (2016).

M. Lukosius et al., Metal-Free CVD Graphene Synthesis on 200 mm Ge/Si(001) Substrates. Acs Applied Materials & Interfaces
8, 33786-33793 (2016).

R. M. Jacobberger, M. S. Arnold, High-Performance Charge Transport in Semiconducting Armchair Graphene Nanoribbons Grown Directly on Germanium. Acs Nano
11, 8924-8929 (2017).

A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium. Nano Letters
18, 898-906 (2018).

Figure 1