Topologically Optimized Copper Pre-Orienting Layer Enabled High-Quality GaN Micropyramid Epitaxy on Amorphous Glass

Heteroepitaxy of single-crystalline GaN on glass represents a promising approach for low-cost, large-area optoelectronics, yet the amorphous nature of glass inherently lacks the long-range atomic order required for crystalline templating. To address this limitation, we introduce a distinctive topologically optimized pre-orienting layer (TOPL) strategy based on Cu (111) thin films, enabling the growth of an AlN (0002) buffer layer and thus achieving high-quality GaN micropyramid array epitaxy on amorphous glass. First, by introducing a disconnected Cu thin film, the grain boundaries during annealing are effectively confined within the non-epitaxial region. This process to a large extent overcomes the polycrystallization of metal templates on amorphous glass. Then, experiments demonstrated that under multiply connected configurations, the Cu (111) surface not only preserves the grain-boundary-confining property but also exhibits notable surface smoothness. Among the evaluated symmetries, the sixfold symmetry structure achieves the optimum atomic-level flatness with a root-mean-square roughness of 0.395 nm. Building upon this TOPL architecture, c-axis-oriented GaN micropyramids were grown via selective area epitaxy. The glass-based GaN micropyramid demonstrates comparable crystalline quality (threading dislocation density from a single lamella: 5.46 × 10⁸ cm^-2) to those grown on sapphire substrates, while exhibiting reduced stress and comparable cathodoluminescence full width at half maximum. Overall, the TOPL strategy presents a promising pathway toward low-cost GaN micropyramid epitaxy on glass substrates.