Modeling and Designing a GaN-Growth Reactor With Halogen-Free Vapor Phase Epitaxy: NH₃ Decomposition at the Catalytic Surface of Components to Replicate Parasitic Polycrystal Formation

Achieving long-duration, large bulk GaN growth is crucial to supply low-cost, high-quality GaN. Halogen-free vapor phase epitaxy (HF-VPE) is a promising method for bulk GaN growth but faces challenges due to severe polycrystals deposition on reactor components, such as the source-gas nozzles, which impedes stable, extended growth. In this study, we developed models to simulate the polycrystal deposition in HF-VPE-GaN growth conditions by including surface reactions of GaN formation and NH3 decomposition. Moreover, we devised conditions for controlling gas flow and interdiffusion to suppress polycrystal deposition around the source-gas nozzles. Experimental results aligned with simulations, showing that increasing the distance between Ga and NH₃ nozzles and replacing the sheath gas from H₂ to N₂ effectively minimized polycrystal formation. The findings confirm that reducing NH₃ concentration through catalytic surface decomposition on refractory components is crucial to polycrystal suppression. Optimizing nozzle dimensions and gas species synergistically controls the gas flow and interdiffusion. The constructed models contribute to advancing the design of polycrystal suppressive structures and conditions for long-duration bulk GaN growth.