A self-assembled graphene nanomask for the epitaxial growth of nonplanar and planar GaN

Due to the unique properties of two-dimensional (2D) materials, van der Waals epitaxy or the remote epitaxy of nonplanar and planar materials on 2D materials plays an important role in various applications; however, it is often limited by low crystal quality due to misorientation in nonplanar materials or grain boundaries and high threading dislocation densities in planar materials. Selective area growth (SAG), in which orientations are concordant, grain boundaries can be avoided, and threading dislocations can be annihilated, is an effective way to overcome this limitation. It is believed that microscale materials are the predominant masks for SAG, and the nanoselective area growth (NSAG) technology is superior to SAG as it can allow the mechanical exfoliation of the epilayer from the substrate. Herein, we demonstrated the fabrication of architectural GaN nanostructures by the self-assembly NSAG (SNSAG) technology using multilayer graphene (MLG) as a nanomask. The microstructure and optical properties were characterized by scanning electron microscopy, transmission electron microscopy, cathodoluminescence, and micro-Raman and micro-photoluminescence spectroscopy techniques for evidencing the high-quality GaN nanostructures; moreover, high-quality, stress-relaxation GaN films were grown by SNSAG on MLG/SiC and mechanically exfoliated from the substrate for obtaining free-standing GaN. This technique enables the integration of any nonplanar and planar semiconductor material with graphene for extensible applications.