Scalable thru-hole epitaxy of GaN through self-adjusting $h$-BN masks via solution-processed 2D stacks

Abstract: Selective epitaxy on 2D-material masks is a promising pathway for achieving localized, defect-suppressed GaN growth, but conventional 2D transfer processes limit scalability and interface control. Here, we demonstrate a thru-hole epitaxy (THE) method that enables vertically connected and laterally overgrown GaN domains through a spin-coated, solution-processed stack of hexagonal boron nitride ($h$-BN) flakes. The disordered $h$-BN mask exhibits a self-adjusting structure during growth, which locally reconfigures to allow percolative precursor transport and coherent GaN nucleation beneath otherwise blocking layers. Comprehensive structural analyses using scanning electron microscopy, Raman mapping, and high-resolution transmission electron microscopy confirm both the presence of epitaxial GaN beneath the h-BN and suppression of threading dislocations. This strategy eliminates the need for patterned 2D mask transfers and demonstrates a scalable route to selective-area GaN growth on arbitrary substrates, relevant to future micro-LED and photonic integration platforms.