On the vacancy diffusion from ammonothermally grown GaN to GaN epilayer

The stability and transport of native point defects at the interface between ammonothermally grown GaN substrates and MOVPE-grown GaN epilayers remain insufficiently understood, despite their relevance for high-performance GaN electronics. In this work, we investigate the long-standing question of whether native vacancies can diffuse from low-dislocation-density ammonothermal GaN into subsequently grown epitaxial layers. A combination of complementary techniques—including Secondary Ion Mass Spectroscopy (SIMS), C–V profiling, photoluminescence, Raman spectroscopy, and detailed modelling of variable-energy positron annihilation spectroscopy (VEPAS)—is employed to resolve vacancy distributions with high depth sensitivity. Our results consistently show that vacancy-related defects do not propagate from the substrate into the MOVPE epilayer. Instead, we identify a highly compensated interfacial region extending several hundred nanometres into the ammonothermal GaN. This region electrically decouples the epilayer from the substrate and generates built-in electric fields that may influence carrier transport and device behavior. These findings provide new insight into defect behaviour at GaN heterointerfaces and have direct implications for the optimization of ammonothermal GaN substrates for power and optoelectronic devices.