Impact of Fluid Flow on GaN Crystal Growth Modes Using the Na-Flux Method on Patterned Substrates

The impact of fluid flow on the growth mode of GaN crystals during liquid-phase epitaxial (LPE) growth using the Na-flux method was investigated through a combination of experimental and numerical approaches. MOCVD-GaN patterned substrates were used as seed crystals with two different seed placements: vertical and tilted. A detailed analysis was performed on both the morphological features of the crystal and the characteristics of the fluid flow. Under the vertical placement condition, the fluid flow exhibits a uniform laminar flow state, with the fluid flowing in a direction parallel to the bottom of the seed. This results in a regularly symmetric hexagonal pyramidal morphology of the GaN crystal. In contrast, under the tilted placement condition, the fluid flows in a tilted direction along the [1̅1̅20] crystal orientation of the seed. This promotes coalescence along the [1̅1̅20] direction, resulting in a ridge-like structure aligned along the [1̅1̅20] direction of as-grown GaN crystals. By precisely adjusting and designing the direction and velocity of the fluid flow, the crystal growth mode can be effectively modulated to optimize the morphology of the crystal. These findings not only advance the fundamental understanding of hydrodynamic phenomena in crystal growth but also offer new insights and strategies for process optimization and growth control.