Influence of temperature on growth of graphene on germanium

Growth of high-quality graphene on germanium is to date only reported at growth temperatures near the substrate melting point. Direct integration of graphene growth into technological processes would, however, require a significantly lower growth temperature. Accordingly, we investigated the influence of growth temperature on the quality of graphene on Ge(001), Ge(110), and Ge(111). We found that increased defect density as indicated by Raman spectroscopy correlates with topographically protruding carbon defect clusters as indicated by scanning tunneling microscopy. The Raman quality of graphene on Ge(001) and Ge(110) grown at 850 °C is clearly limited by defects within the relatively large grains and not by grain boundaries, whereas the quality of graphene on Ge(111) additionally suffers from small grain size. We explain the decreased graphene quality by too weak substrate-mediated etching of defective carbon structures. Finally, we discuss potential ways to increase the rate of carbon etching.