Pseudo-Graphene on SiC for High-Quality GaN Membrane

Free-standing membranes are building blocks for various electronic and photonic devices since they can provide a large degree of freedom for the platform. Besides, along with their extraordinary material properties, single-crystalline free-standing membranes can reduce material costs. In this regards, fabrication of free-standing membranes requires successful separation of active materials from various types of substrates. However, conventional approaches have exhibited challenges in the sense of poor interface quality, complexity in choice of materials, and such. Recently, remote epitaxy has arisen as a new technology that can overcome current limitations enabling both high crystal quality and simplicity in the materials. In remote epitaxy, electrostatic potential is not completely screened by 2D material (e.g. graphene) inserted as a releasing layer between the substrate and the active material. In other words, remote interaction between two materials results in the successful epitaxial growth of the active material such as GaAs or GaN. The quality of 2D material, therefore, is highly crucial in achieving high-quality single-crystalline free-standing membranes.<br/>In this study, we demonstrated a new 2D platform using graphene/SiC in remote epitaxy. We discovered that graphitized SiC has sp²-bonded graphene layer on the very top surface and sp³-bonded pseudo-graphene(pGr) between graphene and SiC. The graphene fully covers pGr providing sufficient van der Waals force above the epitaxial layer, enabling efficient transfer of free-standing membranes without any possible damage. This research includes systematic studies on pGr/SiC used as a releasing layer for free-standing GaAs/GaN membranes.