Free-standing
crystalline membranes are highly desirable owing
to recent developments in heterogeneous integration of dissimilar
materials. Van der Waals (vdW) epitaxy enables the release of crystalline
membranes from their substrates. However, suppressed nucleation density
due to low surface energy has been a challenge for crystallization;
reactive materials synthesis environments can induce detrimental damage
to vdW surfaces, often leading to failures in membrane release. This
work demonstrates a novel platform based on graphitized SiC for fabricating
high-quality free-standing membranes. After mechanically removing
epitaxial graphene on a graphitized SiC wafer, the quasi-two-dimensional
graphene buffer layer (GBL) surface remains intact for epitaxial growth.
The reduced vdW gap between the epilayer and substrate enhances epitaxial
interaction, promoting remote epitaxy. Significantly improved nucleation
and convergent quality of GaN are achieved on the GBL, resulting in
the best quality GaN ever grown on two-dimensional materials. The
GBL surface exhibits excellent resistance to harsh growth environments,
enabling substrate reuse by repeated growth and exfoliation.
Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy.
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