Characterization of GaN layers grown on polycrystalline AlN substrates by hydride vapor phase epitaxy

Gallium nitride (GaN) layers were grown on low-cost polycrystalline aluminum nitride (pc-AlN) substrates by hydride vapor phase epitaxy (HVPE) using a sputtered AlN buffer layer. Cross-sectional scanning electron microscopy (SEM) revealed relatively uniform GaN growth without interfacial voids or delamination, while transmission electron microscopy (TEM) demonstrated recrystallization behavior in the sputtered AlN buffer layer and the formation of a laterally coalesced GaN/AlN interface. Energy-dispersive X-ray spectroscopy (EDS) confirmed Ga- and N-rich composition in the GaN region with minimal Al interdiffusion, indicating a chemically sharp GaN/AlN interface. Atomic force microscopy (AFM) showed a root-mean-square (RMS) surface roughness of 0.39 µm, consistent with the grain structure of the underlying polycrystalline substrate. X-ray diffraction (XRD) confirmed the wurtzite GaN structure with distinct (002) and (102) reflections, reflecting the polycrystalline nature of the GaN layer. Cathodoluminescence (CL) mapping showed localized emission variations associated with grain boundaries, along with near-band-edge (NBE) and deep-level luminescence features. These results demonstrate the feasibility of continuous HVPE growth of GaN on pc-AlN substrates using a sputtered AlN buffer layer, suggesting a pathway for further optimization of GaN growth on cost-effective non-single-crystal AlN platforms.