Epitaxial growth of single-crystal graphene wafers via chemical vapor deposition technique

<sec><p indent="0mm"><?A3B2 tlb=1.23h?><?A3B2 th=9.5p?>Single-crystal graphene wafers have proven to be a competitive candidate material for silicon semiconductor technology, owing to their excellent electrical, thermal, and mechanical properties. Achieving high-quality, single-crystal graphene wafers through controlled growth methods is, therefore, of great significance in graphene-related research, and has been regarded as the key guarantee to bridge graphene materials to high-performance electronic and optoelectrical devices. Among various synthesis methods, chemical vapor deposition (CVD) has demonstrated great advantages to producing graphene films with high quality, controllability, and scalability, making it a mainstream approach for the synthesis of single-crystal graphene wafers. However, to ensure that the synthesized graphene wafers achieve true single-crystallinity, the precise design of catalyst substrates and careful control over the epitaxial behavior of graphene are crucial. Moreover, the strategies for achieving the aligned growth of graphene domains vary significantly depending on the grown substrate and the targeted application. In addition, the underlying mechanism for the epitaxial growth of graphene wafers also differs depending on these factors. Recent years have witnessed rapid development in the CVD-derived graphene wafers on single-crystal metal substrates, covering the state-of-the-art methods for controllable synthesis and up-scale technologies for mass production. Meanwhile, significant breakthroughs have also been achieved in the direct growth of graphene single-crystals on semiconductor and insulating substrates, paving the way for the commercial utilization of graphene materials in electronics, photonics, energy and environment fields. </sec><sec> <?A3B2 tlb=1.23h?><?A3B2 th=9.5p?>In this review, recent progress towards the CVD growth of single-crystal graphene wafers is summarized based on the type of grown substrates, such as metal, semiconductors and insulators. We first discussed the single-crystallization methods for the fabrication of Cu(111) films on sapphire substrates, which is a prerequisite for the subsequent preparation of graphene single crystals and determines the quality of the resulting graphene films. Subsequently, we reviewed recent progress on the growth of single-crystal graphene wafers on Cu(111) and Cu-based alloy(111) substrates, focusing on the advancements made in the elimination of graphene wrinkles and the precise control of graphene thickness. These advancements are critical as they significantly impact the quality and uniformity of the graphene wafers, which in turn affect their performance in electronic applications. Then, we reviewed the progress on the direct fabrication of single-crystal graphene wafers on semiconductor substrates. These approaches avoid the transfer process, which often introduces damage, contamination, and doping to the graphene, thereby preserving its intrinsic properties. In particular, we primarily discussed the growth behavior of graphene domains on single-crystal Ge wafers with different crystal planes, together with underlying epitaxial mechanism. In addition, we reviewed the effective strategies for the synthesis of graphene single crystals directly on insulating substrates, which mainly aim to address the challenges associated with the catalytic inertness of insulating surfaces, such as ultra-high temperature growth and fabrication of catalytic-insulator growth interfaces. Finally, we discussed the development of scalable technologies and advanced equipment for the pilot-scale production of single-crystal graphene wafers, which is essential to reduce production costs for final commercial applications. </sec><sec> <?A3B2 tlb=1.23h?><?A3B2 th=9.5p?>In conclusion, this review highlights the recent progress in the CVD growth of single-crystal graphene wafers on metal, semiconductor, and insulating substrates, focusing on substrate design, epitaxial growth control, and scalable manufacturing technologies. We believe that, the future of single-crystal graphene wafers lies in continuous breakthroughs in fundamental research, scalable technologies, and mass production equipment. With these advancements, single-crystal graphene is potential to become a key material in many cutting-edge applications, particularly in the fields of high-performance electronics and optoelectronics, and thereby accelerates the development of graphene industry. </sec>