Potential of Graphene as a Universal Substrate for Disruptive Epitaxial Devices

石墨烯的二维(2D)碳结构独特地结合了机械灵活性、弱表面键合和六方晶格。当半导体晶体生长在石墨烯上时，其2D薄片有望弹性重塑以适应晶体或热失配，从而能够在任意衬底上生长高质量半导体，而不会出现晶体变形和损伤。这是目前社会上密集研究的主题，但由于尚未达成可行的解决方案，这个问题仍然悬而未决。在石墨烯晶体生长的初始阶段观察到的许多影响令人惊讶，至今仍未完全了解。 高性能半导体器件是通过在兼容的衬底上生长特殊的、薄的、高质量的“外延”层来制造的。然而，基片价格昂贵，来自有限的全球资源，这往往限制了将具有互补性能的材料集成在一起的可能性。 在今天的市场上，性能预期正达到前所未有的水平，迫使该行业设计和生产基于完全不同的晶体结构堆叠的设备，这是外延传统上禁止的条件。应对这一挑战所需的科学和技术仍有待充分发展，而创造能够适应这些极端条件的新型基质是一条很有希望的途径。然而，由于这些特殊基板推高了设备成本并限制了其功能，任何有望进入市场的解决方案都必须具有成本效益和可扩展性。这个挑战引发了这样一个问题：“石墨烯是解决不匹配外延的根本挑战的终极材料吗？” 我的研究计划将把一种多方面的、高潜力的材料(石墨烯)与基本的工业和科学挑战结合在一起，以产生影响。我将通过原创和创新的方法，具体解决III-V在石墨烯上生长的两个主要问题：设计石墨烯的表面能，通过我称之为“锚点成核”的成核过程，增强III-VS材料在石墨烯上的成核。 这将使学生和研究人员参与阐明3D晶体(GaAs、InP、GaN)在2D晶体(即：石墨烯)上成核和生长的物理过程。这里的潜力是巨大的，可以将半导体外延和转移到任意衬底(例如：金属、陶瓷、柔性聚合物)上，用于新一代混合器件，如轻便、灵活的高效太阳能电池，以及在硅上集成III-V器件，从而实现与高速电子和光子学的兼容性。活动的重点将是涉及高效太阳能电池实际演示的成果。

Graphene's two dimensional (2D) carbon structure uniquely combines mechanical flexibility, weak surface bonding and a hexagonal lattice. When semiconductor crystals are grown onto graphene, its 2D sheet is expected to elastically reshape to accommodate crystal or thermal mismatches, enabling growth of high-quality semiconductors on arbitrary substrates, without crystal deformations and impairments. This is currently the subject of intense research in the community, but the question remains open as no viable solution was reached yet. Many of the observed effects during the initial phase of the crystal growth on graphene are surprising and still not fully understood. High performance semiconductor devices are made by growing special, thin, high quality “epitaxy” layers onto compatible substrates. However the substrates are costly and come from limited global resources, which often limit the possibility of integrating materials with complementary properties. In today's market, the performance expectations are reaching unprecedented levels that force the industry to design and produce devices based on stack of radically different crystal structures, a condition traditionally forbidden in epitaxy. The science and technology necessary to face this challenge remains to be fully developed, and the creation of new kinds of substrates, with the ability to accommodate these extreme conditions is a promising avenue. However, since these special substrates drive up device cost and limits its functionalities, any solution that might have hope to access the market must be cost-effective and scalable. This challenge motivated the question: “Is graphene the ultimate material to solve fundamental challenges of mismatched epitaxy?” My research program will bring together a multifaceted, high potential material (graphene) with a fundamental industrial and scientific challenge, to generate impact. I will specifically address the two main issues in III-V growth on graphene through original and innovative approache: engineer graphene's surface energy to enhance the nucleation of III-Vs materials on graphene through a nucleation process that I name “Anchor Point Nucleation”. This will involve students and researchers in work illuminating the physics of nucleation and growth for 3D crystals (GaAs, InP, GaN) onto 2D crystals (i.e: graphene). The potential here is vast, offering epitaxy and transfer of semiconductors onto arbitrary substrates (e.g: metals, ceramics, flexible polymers) for new generations of hybrid devices such as low-weight, flexible high-efficiency solar cells, and integration of III-V devices on Si, enabling compatibility with high speed electronics and photonics. A focus of the activity will be outcomes involving practical demonstrations on high-efficiency solar cells.