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Register a new userHighly Ordered Boron Nitride/Epigraphene Epitaxial Films on Silicon Carbide by Lateral Epitaxial Deposition
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Realizing high-performance nanoelectronics requires control of materials at the nanoscale. Methods to produce high quality epitaxial graphene (EG) nanostructures on silicon carbide are known. The next step is to grow Van der Waals semiconductors on top of EG nanostructures. Hexagonal boron nitride (h-BN) is a wide bandgap semiconductor with a honeycomb lattice structure that matches that of graphene, making it ideally suited for graphene-based nanoelectronics. Here, we describe the preparation and characterization of multilayer h-BN grown epitaxially on EG using a migration-enhanced metalorganic vapor phase epitaxy process. As a result of the lateral epitaxial deposition (LED) mechanism, the grown h-BN/EG heterostructures have highly ordered epitaxial interfaces, as desired in order to preserve the transport properties of pristine graphene. Atomic scale structural and energetic details of the observed row-by-row, growth mechanism of the 2D epitaxial h-BN film are analyzed through first-principles simulations, demonstrating one-dimensional nucleation-free-energy-barrierless growth. This industrially relevant LED process can be applied to a wide variety of van der Waals materials.
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This article presents a review of epitaxial graphene on silicon carbide, from fabrication to properties, put in the context of other forms of graphene.
The materials science of graphene grown epitaxially on the hexagonal basal planes of SiC crystals is reviewed. We show that the growth of epitaxial graphene on Si-terminated SiC(0001) is much different than growth on the C-terminated SiC(000 -1) surface, and discuss the physical structure of these graphenes. The unique electronic structure and transport properties of each type of epitaxial graphene is described, as well as progress toward the development of epitaxial graphene devices. This materials system is rich in subtleties, and graphene grown on the two polar faces differs in important ways, but all of the salient features of ideal graphene are found in these epitaxial graphenes, and wafer-scale fabrication of multi-GHz devices already has been achieved.
Two-dimensional crystals are an important class of materials for novel physics, chemistry, and engineering. Germanane (GeH), the germanium-based analogue of graphane (CH), is of particular interest due to its direct band gap and spin-orbit coupling. Here, we report the successful co-deposition growth of CaGe2 films on Ge(111) substrates by molecular beam epitaxy (MBE) and their subsequent conversion to germanane by immersion in hydrochloric acid. We find that the growth of CaGe2 occurs within an adsorption-limited growth regime, which ensures stoichiometry of the film. We utilize in situ reflection high energy electron diffraction (RHEED) to explore the growth temperature window and find the best RHEED patterns at 750 {deg}C. Finally, the CaGe2 films are immersed in hydrochloric acid to convert the films to germanane. Auger electron spectroscopy of the resulting film indicates the removal of Ca and RHEED patterns indicate a single-crystal film with in-plane orientation dictated by the underlying Ge(111) substrate. X-ray diffraction and Raman spectroscopy indicate that the resulting films are indeed germanane. Ex situ atomic force microscopy (AFM) shows that the grain size of the germanane is on the order of a few micrometers, being primarily limited by terraces induced by the miscut of the Ge substrate. Thus, optimization of the substrate could lead to the long-term goal of large area germanane films.
We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between.
Spin information processing is a possible new paradigm for post-CMOS (complementary metal-oxide semiconductor) electronics and efficient spin propagation over long distances is fundamental to this vision. However, despite several decades of intense research, a suitable platform is still wanting. We report here on highly efficient spin transport in two-terminal polarizer/analyser devices based on high-mobility epitaxial graphene grown on silicon carbide. Taking advantage of high-impedance injecting/detecting tunnel junctions, we show spin transport efficiencies up to 75%, spin signals in the mega-ohm range and spin diffusion lengths exceeding 100 {mu}m. This enables spintronics in complex structures: devices and network architectures relying on spin information processing, well beyond present spintronics applications, can now be foreseen.
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