Graphene was shown to reveal intriguing properties of its relativistic two-dimensional electron gas; however, its implementation to microelectronic applications is missing to date. In this work, we present a comprehensive study of epitaxial graphene on technologically relevant and in a standard CMOS process achievable Ge(100) epilayers grown on Si(100) substrates. Crystalline graphene monolayer structures were grown by means of chemical vapor deposition (CVD). Using angle-resolved photoemission spectroscopy and in situ surface transport measurements, we demonstrate their metallic character both in momentum and real space. Despite numerous crystalline imperfections, e.g., grain boundaries and strong corrugation, as compared to epitaxial graphene on SiC(0001), charge carrier mobilities of 1 × 10 4 cm 2 / Vs were obtained at room temperature, which is a result of the quasi-charge neutrality within the graphene monolayers on germanium and not dependent on the presence of an interface oxide. The interface roughness due to the facet structure of the Ge(100) epilayer, formed during the CVD growth of graphene, can be reduced via subsequent in situ annealing up to 850 °C coming along with an increase in the mobility by 30%. The formation of a Ge(100)−(2 × 1) structure demonstrates the weak interaction and effective delamination of graphene from the Ge/Si(100) substrate.

We present the electronic and structural properties of monolayer WSe2 grown by pulsed-laser deposition on monolayer graphene (MLG) on SiC. The spin splitting in the WSe2 valence band at K was ∆SO = 0.469 ± 0.008 eV by angle-resolved photoemission spectroscopy (ARPES). Synchrotron-based grazing-incidence inplane X-ray diffraction (XRD) revealed the in-plane lattice constant of monolayer WSe2 to be aWSe 2 = 3.2757 ± 0.0008Å. This indicates a lattice compression of −0.19% from bulk WSe2. By using experimentally determined graphene lattice constant (aMLG = 2.4575 ± 0.0007Å), we found that a 3×3 unit cell of the slightly compressed WSe2 is perfectly commensurate with a 4×4 graphene lattice with a mismatch below 0.03%, which could explain why the monolayer WSe2 is compressed on MLG. From XRD and first-principles calculations, however, we conclude that the observed size of strain is negligibly small to account for a discrepancy in ∆SO found between exfoliated and epitaxial monolayers in earlier ARPES. In addition, angle-resolved, ultraviolet and X-ray photoelectron spectroscopy shed light on the band alignment between WSe2 and MLG/SiC and indicate electron transfer from graphene to the WSe2 monolayer. As further revealed by atomic force microscopy, the WSe2 island size depends on the number of carbon layers on top of the SiC substrate. This suggests that the epitaxy of WSe2 favors the weak van der Waals interactions with graphene while it is perturbed by the influence of the SiC substrate and its carbon buffer layer. arXiv:1912.04770v1 [cond-mat.mtrl-sci]