Freestanding GaN Substrate Enabled by Dual-Stack Multilayer Graphene Via Hydride Vapor Phase Epitaxy

The freestanding GaN substrate has a great potential to homo-epitaxy of optoelectronic and electronic devices with high reliability and performances. Here, we realized the growth of freestanding bulk GaN on dual-stack multilayer graphene as an insertion layer by the hydride vapor phase epitaxy (HVPE) method. Stacked multilayer graphene was fabricated on copper foil using chemical vapor deposition (CVD), following the overlap of top and bottom layers of graphene after removing the copper. Based on Raman spectra and X-ray photoelectron spectroscopy (XPS) experiments, it is found that the dual-stack structure of multilayer graphene is crucial for the self-separation of GaN substrate from sapphire. The exfoliation was attributed to the weak interaction force between the dual-stack multilayer graphene. This study can provide an efficient, practical, and mass-producible technique to fabricate freestanding GaN substrates, which exhibit immense application potential for the nitridebased optoelectronic and electronic devices.