Large-scale uniform graphene growth was achieved by suppressing inhomogeneous carbon segregation using a single domain Ru film epitaxially grown on a sapphire substrate. An investigation of how the metal thickness affected growth and a comparative study on metals with different crystal structures have revealed that locally enhanced carbon segregation at stacking domain boundaries of metal is the origin of inhomogeneous graphene growth. Single domain Ru film has no stacking domain boundary, and the graphene growth on it is mainly caused not by segregation but by a surface catalytic reaction. Suppression of local segregation is essential for uniform graphene growth on epitaxial metal films.

The nature of graphene/substrate interfaces needs to be understood to improve the crystalline quality of graphene films grown with chemical vapor deposition (CVD). We have theoretically investigated the potential-energy surface (PES) of graphene on catalyst transition-metal surfaces. The profile of PES highly depends on the type of underlying metals; the orders of the peak-to-valley (PV) values of PES are Cu < Ni < Co (3d), Pd < Rh < Ru (4d), and Pt < Ir < Os (5d). High PV values were found to be provided by metals with d-band close to the Dirac point of graphene. Our results indicate that the d-band of catalyst metals greatly influences the PES profile of graphene on the metals, which should be helpful for further understanding of the graphene/metal interfaces and its behavior in CVD growth process.

Si 1−x−y Ge x C y crystals were grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD) using Si2H6, GeH4, and SiH3CH3 as source gases. Although the total C content in the grown crystals increased with increasing the partial pressure of SiH3CH3 gas, the substitutional C content saturated at a certain value. The maximum substitutional C content was found to change depending on the Ge content. As the Ge content was increased from 13 to 35 at. %, the maximum substitutional C content linearly decreased from 2.0 to 0.8 at. %. These results clearly demonstrate that the existence of Ge atoms prevents the substitutional incorporation of C atoms in Si1−x−yGexCy growth by CVD.

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We attempted to prepare Ge1-y C y alloys by implantation of C atoms into Ge crystals and post-annealing. For samples annealed at temperatures higher than 450°C, X-ray diffraction (XRD) spectra indicated that the Ge1-y C y alloys were successfully prepared. The highest substitutional C content was about 1 at.%. The optimum annealing temperature to incorporate C atoms into the substitutional sites was 450–500°C. We also investigated the dependence of the Raman intensity of the Ge–C local mode on the substitutional C content. The intensity of the Ge–C local mode was found to increase in proportion to the substitutional C content. Furthermore, the relationship between Ge–C peak intensity and substitutional C content was relatively in good agreement with that theoretically predicted.

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The incorporation of C into Si1-x Ge x alloys contributes to enlarging the critical layer thickness and to improving the thermal budget. It also realizes a narrower bandgap with compensated strain. These effects would introduce good performance at high frequency in the devices. We fabricate heterojunction bipolar transistors (HBTs) with an Si1-x-y Ge x C y base layer using ultrahigh-vacuum chemical vapor deposition (UHV-CVD) technology. The bandgaps of Si1-x-y Ge x C y base layers are measured by the evaluation of the collector current dependence on temperature. The strain of the pseudomorphic Si1-x-y Ge x C y layer is also extracted by an analysis of the X-ray diffraction spectra. Good flexibility of Si1-x-y Ge x C y alloy is shown for the bandgap and strain engineering. The devices using the excellent characteristics of Si1-x-y Ge x C y alloy have numerous applications for wireless telecommunications.

The local vibration mode of substitutional C atoms (C-LVM) in high-quality Si1-x-y Ge x C y crystals was studied by infrared absorption spectroscopy. The peak intensity and full width at half maximum of C-LVM were found to change depending on Ge content as well as substitutional C content. However, the integrated intensity of C-LVM exhibited a linear dependence on the substitutional C content. These results demonstrate that the effective charge of substitutional C atoms in Si1-x-y Ge x C y crystals is independent of their atomic configurations. Moreover, the present results clearly indicate that the substitutional C content can be estimated from the integrated intensity of C-LVM.