Freestanding GaN Membranes via Lattice Inheriting from Nearly Single-Crystalline Bilayer Graphene

Freestanding gallium nitride (GaN) membranes can extend the applications of GaN to more functional devices through heterogeneous integration. Two-dimensional (2D) materials provide a versatile platform for the preparation of a freestanding ultrathin membrane. However, fabrication of a freestanding GaN membrane with the aid of 2D materials presents a challenge at the GaN/2D interface: keeping strong epitaxial interactions for epitaxy while contrarily ensuring weak interactions for intact exfoliation. Here, an approach for achieving a freestanding GaN membrane is demonstrated via epitaxy of GaN on chemical vapor deposition (CVD)-grown nearly single-crystalline bilayer graphene/sapphire, followed by intact exfoliation. Single-crystalline GaN is realized by inheriting the lattice orientation of graphene in a quasi-van der Waals epitaxy mode and modulating the growth kinetics of III-nitrides. Subsequently, controllable exfoliation is realized at the bilayer graphene interface by adjusting the interface adhesion. The achieved freestanding GaN membrane maintains a high quality comparable to that of GaN on a rigid substrate. This work offers a promising strategy for the fabrication of a high-quality freestanding GaN membrane for diverse device applications.