An investigation of a catalyst free PECVD nanocrystalline graphene/graphite on insulator

Abstract

The unique electrical and optical properties of graphene have attracted application as transparent electrodes, transistors and photodetectors. However, the small flake size of mechanical exfoliated graphene has limited its scalability to large area production. Recently, large area graphene is produced through chemical vapour deposition (CVD) and epitaxial growth method. CVD of graphene on insulator or metal-catalyst is considered low cost and process flexible. This is because graphene film quality and deposition rate can be controlled through process parameters such as temperature, gas flow rate and gas mixture. Large area CVD graphene on metal-catalyst such as Ni or Cu is amongst other established method but the need for processing steps, such as film transfer and metal etching can ultimately damage the graphene and affect device performance. Therefore, the research attention is now focused on catalyst free CVD graphene process on insulator materials such as silicon dioxide (SiO₂).
In this work, the nanocystalline graphene/graphite (NCG) films are synthesised in a mixture of methane (CH₄) and hydrogen (H₂) environment using radio frequency chemical vapour deposition (RF PECVD) without metal transition catalyst, deposited directly onto 150 mm diameter silicon wafer with an insulating substrate, such as SiO₂, is presented. The as-deposited NCG films properties depend on deposition conditions such as growth temperature, growth time, pressure, mixtures or flow rates of precursor, RF power and substrate material. Initially, the growth temperatures are varied in the range of 600 °C to 850 °C, while keeping other deposition parameters unchanged, and subsequently the properties of the as-deposited NCG film is studied. The nanocrystalline nature of as-deposited film are analysed based on their Raman spectra, whereas the film thickness and sheet resistances are characterised using ellipsometry spectroscopy and a simple four point probe measurements respectively.
The electrical properties of the NCG films are performed using I-V measurement on a simple two terminal device with titanium/nickel (Ni/Ti) contacts. Transmission line method (TLM) structures with Ni/Ti probe pads are also fabricated for contact and sheet resistances measurement purposes.

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ORCID for Harold Chong: orcid.org/0000-0002-7110-5761

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