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The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition-metal-treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around 450−500 °C. From the chemical reaction between SiC and thin films of Fe or Ru, sp 3 carbon is liberated from the SiC crystal and converted to sp 2 carbon at the surface. The quality of the graphene is demonstrated by using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate are verified by using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene-based device structures.

GaAsPBi is a new class of quaternary III-V compounds that extends the concept of band gap engineering on GaAs with potentials for lattice matching and excellent temperature stability. The alloy has so far been grown only by metalorganic vapor phase epitaxy and this work represents the first epitaxial results of the alloy grown by molecular beam epitaxy (MBE), an alternative technique and better suited for low-temperature processes involving Bismuth. Crystalline quality of the alloys is probed by high-resolution x-ray diffraction and photoluminescence (PL) which show that smooth and optically active films can be grown in limited parameter windows. Temperature-dependent PL shows that the 200 nm, MBE-grown GaAs 0.38 P 0.44 Bi 0.18 film (the composition estimated using x-ray photoelectron spectroscopy) has a band gap temperature stability close to that of GaAsBi, and superior to GaAs. The role of Bi in the quaternary alloy is complicated: Bi not only gets incorporated into the growing film but also enhances the P molar fraction. Based on this insight, strategies for growing GaAsPBi epilayers which are lattice-matched to GaAs are described, potentially affecting many important III-V based heterostructures such as lasers, light-emitting diodes, and solar cells.

Quaternary alloy GaAsPBi is a novel III–V compound with attractive optical properties and can in principle be grown lattice-matched to GaAs. However, the practical realization of the alloy by metal-organic vapor phase epitaxy and molecular beam epitaxy (MBE)—the two main growth technologies—is fraught with difficulties. Here, using standard solid-source MBE, GaAsPBi films, and GaAsPBi/GaAs multiple quantum wells (MQW) have been grown lattice-matched to (001) GaAs. The structural integrity of the films/MQW is investigated and confirmed by various in- and ex-situ diffraction and spectroscopic techniques. All GaAsPBi structures—films and MQWs—are luminescent at room temperature. Photoluminescence shows that all the samples exhibit an S-shape temperature dependency, indicating strong localizations. Of most significance to practical applications is the observation that the emission from GaAsPBi MQWs is more efficient than their non-quantum well (QW) counterparts (up to 30× at room temperature). These results confirm the long-known benefits of carrier confinements by QWs, demonstrated here for the first time in the GaAsPBi-based system despite the challenge of the crystal growths.

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