High-Mobility Epitaxial Graphene on Ge/Si(100) Substrates

Abstract

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.

Surface Transport Properties of Pb-Intercalated Graphene

“…In fact, the sheet resistance R sh for the intercalated graphene is as low as 10 Ω/ , i.e., the charge carrier mobility is within the Drude model µ = 9 × 10 5 cm 2 V −1 s −1 , assuming that only the small hole concentration p in graphene, determined by ARPES (see above), is attributing to the transport. For epitaxially grown graphene on Ge/Si(100) similarly high charge carrier mobility values were found [36]. Despite the structural imperfections, mainly the charge neutrality in graphene is responsible for this comparably high value.…”

“…The transport experiments were performed by means of a 4-tip STM/SEM system (Omicron Nanoprobe). Details are described elsewhere [36]. In addition, we performed X-ray and angle resolved photoelectron spectroscopy (XPS, ARPES).…”

Momentum microscopy of Pb-intercalated graphene on SiC: charge neutrality and electronic structure of interfacial Pb

“…Corresponding only to a single charge carrier per ≈ 700, 000 C atoms, this vividly highlights the essential charge neutrality of Pb-QFMLG. The latter is interesting in terms of the overall limited carrier mobilities of epigraphene, which have often been ascribed to interactions with its substrate as evidenced by, e.g., finite doping [6,52,53]. Note that epigraphene is generally doped via (i) the spontaneous polarization for hexagonal SiC [54], (ii) excess-charge transfer for n-type SiC [55], and (iii) element-specific charge transfer from intercalated layers [8][9][10][11][12][13][14][15][16][17].…”

Surface Engineering of Substrates for Chemical Vapor Deposition Growth of Graphene and Applications in Electronic and Spintronic Devices

“…Moreover, by annealing at 850 °C, the formation of Ge hut clusters on Ge(001) during the CVD process was eliminated, which was advantageous to the carriers mobility enhancement in graphene. 106 Briefly, Ge single crystal exhibits an important potential not only in the semiconductor industry but also in the preparation of graphene. Therefore, Ge has a broad prospect for the synthesis of graphene.…”

“…Finally, large-area single-crystal graphene film was achieved with the growth time increasing (Figure i). Moreover, by annealing at 850 °C, the formation of Ge hut clusters on Ge(001) during the CVD process was eliminated, which was advantageous to the carriers mobility enhancement in graphene . Briefly, Ge single crystal exhibits an important potential not only in the semiconductor industry but also in the preparation of graphene.…”