The nonnegligible role of gases during the synthesis of graphene/silicon carbide composites

<sec><p indent="0mm">As the semiconductor industry approaches the end of the Moore Index roadmap, there is an increasing need to explore new materials. This has led us to focusing on non-traditional materials with unique physical and chemical properties, such as graphene. Graphene, the thinnest carbon material with sp²-bonded carbon atoms arranged in a honeycomb lattice, exhibits exceptional morphological, electronic, and optical properties, which have stimulated significant scientific and industrial interest. Silicon carbide (SiC), one of the typical representatives of the third-generation semiconducting materials, possesses high thermal conductivity, low thermal expansion coefficient and excellent wearability. SiC wafers are highly suitable semiconducting materials for high-temperature, high-frequency, high-radiation and high-power electronic devices. Additionally, SiC fibers and powders, known for their high-temperature resistance and electromagnetic wave absorption properties, continue to be valuable in thermal protection materials and aerospace applications. By depositing continuous graphene films onto traditional SiC substrates, highly competitive thermal, mechanical, electrical, and other functionalities can be introduced. The integration of graphene with SiC has given rise to a novel class of materials, significantly expanding their applications in electronic devices, aerospace, and various other fields. </sec><sec> Although the preparation of graphene/SiC composites has consistently attracted significant attention, achieving high-quality, uniformly controlled graphene layers directly on SiC substrates remains a challenge. Currently, the main methods for <italic>in-situ</italic> growth of graphene on SiC substrates are chemical vapor deposition (CVD) and silicon carbide epitaxy. Graphene grown by these two methods typically exhibits larger domains and higher charge carrier mobility. The CVD method requires carbon-containing precursors for the preparation of graphene making the gas-phase reactions and mass transport processes critical. Compared to CVD, the uniformity of graphene layers grown by silicon carbide epitaxy is generally lower and the growth temperature is higher. This is mainly due to the less precise control over synthesis parameters and the difficulty in manipulating graphene quality through factors, such as face polarity, off-cut angle, polytype, and type of intercalant. However, controlling sublimation rates by introducing silicon or by flowing an inert gas over the hot SiC surface can improve graphene quality. Thus, gases play a nonnegligible role during the synthesis of graphene on SiC substrates. </sec><sec> This paper focuses specifically on the gas components involved in the preparation process of graphene/SiC composites. We review the various roles of gases during pre-, middle-, and post-stages of graphene growth on SiC substrates, including etching and modification of SiC substrates, and the facilitation of graphene growth and decoupling. A smooth SiC surface with uniform steps, which is crucial for high-quality graphene growth, can be achieved by etching with various gases. Modifying SiC substrates is an effective approach for synthesizing heterostructures. Gases significantly impact the quality of graphene, whether they are directly involved in the reaction or not. Additionally, decoupling is a key method for obtaining quasi-free-standing graphene on SiC substrates. This comprehensive review covers all key steps in the preparation of graphene/SiC composites and provides new insights into an integrated approach for their development. It highlights the significance of gases in the composite preparation process, identifies challenges, and outlines future directions for research and development. </sec>