SiGe-intercalated graphene on SiC(0001): Interfacial structures and graphene doping depending on coverage and composition ratio of the alloy

To find out the relation between the charge transfer doping of quasi-free-standing monolayer graphene (QFMLG) formed on 6H-SiC(0001) and the structures of the intercalated SiGe alloy film, Ge atoms were intercalated additionally/substitutionally under QFMLG above the already-built bilayer Si film with a coverage V V of 1.2 ML. When 0.4-ML Ge is additionally intercalated, the SiGe film with a 31 x 2 3 structure is generated and induces weakly n-doped QFMLG whose Dirac point (ED) is at 0.04 eV below the Fermi level (EF). When the V V additionally intercalated Ge amount is over 0.6 ML, the SiGe film with the 2x 1.5n 3 and/or 4x 3 3 structure composed of adatoms and a bilayer is formed below QFMLG. It turns out that Ge atoms preferentially occupy the top layer, while Si atoms occupy the bottom layer. Once a well-ordered trilayer film is formed at a total Si and Ge coverage of 2.3 MLs, though the concentration of Ge is gradually increased by the substitution of Ge atoms for Si atoms, the ED of QFMLG is fixed at 0.20 eV above the EF. Such a result confirms that the amount of charge transferred from the well-ordered trilayer SiGe film to QFMLG is irrelevant to the composition ratio.

Automated summary

The relation between charge transfer doping in quasi-free-standing monolayer graphene (QFMLG) and the structure of intercalated SiGe alloy films formed on 6H-SiC(0001) was investigated. It was found that when 0.4-ML Ge was additionally intercalated, a SiGe film with a 31 x 2 3 structure was generated, leading to weakly n-doped QFMLG. Conversely, when the amount of additionally intercalated Ge exceeded 0.6 ML, a SiGe film with the 2x 1.5n 3 and/or 4x 3 3 structure was formed below QFMLG. The results showed that the charge transferred from the SiGe film to QFMLG was independent of the composition ratio.