EFRI 2-DARE: Phosphorene, an Unexplored 2D High-mobility Semiconductor

随着半导体芯片在计算机、手机、汽车、家电等领域的广泛应用，功能更强、效率更高的半导体芯片在降低电能消耗、延长便携式电子产品的电池寿命等方面可以产生深远的社会影响。如今，每个半导体芯片可能包含数十亿个由最流行的半导体硅制成的晶体管。然而，随着晶体管变得更小、更薄，以便更多的晶体管可以塞到同一芯片上，以更快的速度执行更多的功能，硅基晶体管迟早会遇到量子力学规定的物理限制。硅的物理限制将导致晶体管无法有效地开启和关闭，芯片消耗更多电力，运行更热。为了解决硅的物理限制，科学家们探索了新材料，如由单层碳原子组成的石墨烯，作为制造非常小、非常薄的晶体管的硅的替代品。然而，尽管石墨烯允许电子在晶体管中高度移动，但石墨烯缺乏可用于有效开启和关闭晶体管的能隙。石墨烯的这一缺点促使科学家探索其他原子层状材料，如具有能隙的过渡金属双卤化物，但事实证明，它们有一个不同的缺点，即允许电子只有低迁移率。为了解决原子层状材料的这一困境，最近发现由单层磷原子组成的磷烯既具有高电子迁移率，又具有相当大的能隙。因此，磷烯是未来一代半导体芯片中很有前途的硅替代物。为此，来自普渡大学、利哈伊大学和密歇根州立大学的一组科学家提议探索磷烯，它有可能克服硅以及其他二维原子层状材料的挑战，用于超大规模薄体晶体管应用，从而改变电子行业。将使用一种协作和高度集成的跨学科方法来解决三个主要领域：1)通过剥离探索磷烯，重点放在电学和光学性质以及器件应用上；2)与政府和工业实验室合作，通过化学气相沉积和纳米制造进行合成；以及3)第一原理建模，以指导实验和解释结果。作为唯一可以像石墨烯一样剥离的其他元素材料，磷烯作为未来一代设备的基础材料代表着一个独特的机会。通过剥离进行的初步探索将指导开发高质量、无缺陷的材料和工艺，使其能够安全轻松地集成到设备架构中。此外，磷烯高度折叠的结构决定了每一层都由两个紧密结合的原子层组成？一种可用于开发大规模化学气相沉积制造工艺的特性。这种褶皱结构也使磷烯具有高度的各向异性？一种可用于热电应用的特性。为了降低磷烯对环境的敏感性，并探索其他新的结构和性质，将探索磷烯与石墨烯、六方氮化硼、二硫化钼或其他硫化物和氧化物之间的异质结。例如，与大多数其他原子层状材料不同，磷烯自然是p型的，p型磷晶体管可以与n型二硫化钼晶体管结合，形成能效高的互补电路和隧道晶体管。此外，块状黑磷的直接禁带宽度为0.3 eV，这使其成为一种有用的元素红外探测器。当黑磷被减薄为单一的磷层时，禁带宽度单调增加到2 eV以上。这是一种可用于制造高效太阳能电池和可调谐光电探测器的财产。该奖项由空军科学研究办公室(AFOSR)共同资助

As semiconductor chips are widely used in computers, phones, automobiles, appliances, etc., more capable yet more efficient semiconductor chips can have profound societal impact such as in reducing electric power consumption and in prolonging the battery life of portable electronics. Today, each semiconductor chip may contain billions of transistors that are made of silicon ‒ the most popular semiconductor. However, as transistors are made smaller and thinner so that more of them can be crammed on the same chip to perform more functions at a faster speed, silicon-based transistors will sooner or later run into physical limitations dictated by quantum mechanics. The physical limitations of silicon will cause transistors to fail to turn on and off efficiently and chips to consume more power and run hotter. To address the physical limitations of silicon, scientists have explored new materials such as graphene, made of a single layer of carbon atoms, as an alternative to silicon in making very small and very thin transistors. However, although graphene allows electrons to be highly mobile in a transistor, graphene lacks an energy gap that could be used to turn the transistor on and off efficiently. This shortcoming of graphene has motivated scientists to explore other atomic-layered materials such as transition-metal dichalcogenids which have an energy gap, but they turned out to have a different shortcoming in allowing electrons to have only low mobility. To solve this dilemma of atomic-layered materials, phosphorene, made of a single layer of phosphorus atoms, was recently discovered to have both a high electron mobility and a sizable energy gap. Thus, phosphorene is a promising replacement for silicon in future-generation semiconductor chips. To this end, a team of scientists from Purdue University, Lehigh University and Michigan State University propose to explore phosphorene which can potentially overcome the challenges of silicon as well as other two-dimensional atomic-layered materials for ultra-scaled thin-body transistor applications thereby transforming the electronics industry. A collaborative and highly integrated interdisciplinary approach will be used to address three thrust areas: 1) exploration of phosphorene by exfoliation with focus on electrical and optical properties and device applications, 2) synthesis by chemical vapor deposition and nanomanufacturing in collaboration with government and industry labs, and 3) first-principles modeling to guide experiments and to interpret the results. Being the only other elemental material that can be exfoliated like graphene, phosphorene represents a unique opportunity as the basic material for future-generation devices. The initial exploration through exfoliation will guide the development for high-quality, defect-free materials and processes that enable safe and easy integration into device architectures. Additionally, the highly puckered structure of phosphorene dictates that each single layer comprises two tightly bonded atomic layers ? a property that can be exploited to develop a large-scale chemical vapor deposition manufacturing process. The puckered structure also makes phosphorene highly anisotropic ? a property that can be exploited for thermoelectric applications. To reduce the environmental sensitivity of phosphorene and to explore other novel architectures and properties, heterojunctions between phosphorene and graphene, hexagonal boron nitride, molybdenum disulfide, or other chalcogenides and oxides will be explored. For example, unlike most other atomic-layered materials, phosphorene is naturally p-type, and p-type phosphorene transistors can be combined with n-type molybdenum-disulfide transistors to form energy-efficient complementary circuits and tunneling transistors. Moreover, black phosphorus in bulk form has a direct band gap of 0.3 eV, which makes it a useful elemental infrared detector. When black phosphorus is thinned to a single phosphorene layer, the band gap increases monotonically to above 2 eV ? a property that can be exploited for efficient solar cells and tunable photodetectors.This award is co-funded by the Air Force Office of Scientific Research (AFOSR)