Simultaneous growth of multiple GaN crystals and numerical optimization in the Na-flux liquid phase method

Abstract

A total of 11 GaN crystals, each measuring 10 × 13 mm², were successfully grown simultaneously on vertical multiple MOCVD-GaN thin film seeds utilizing the Na-flux liquid-phase epitaxy method. All the crystals are highly consistent and evident in their uniform cellular morphology. The top-to-bottom variation in sample thickness is related to their location in the crucible. Samples situated at the most marginal region of the solution show a consistent monotonic increase in thickness from the bottom to the top. In contrast, those located in the sub-marginal regions demonstrate a significant decrease in thickness along the longitudinal axis. Conversely, samples found in the more central regions maintain relatively uniform thickness profiles from the bottom to the apex, with the most central specimen notably displaying perfect uniformity in thickness across the entire height. The bottom-up variation of sample thickness is consistent with the bottom-up trend of the longitudinal nitrogen concentration near the surface of the seed crystals in solution. The thickness variation from top to bottom in all samples is at most 160 μm, which is approximately 8 μm less per millimeter compared to the previous Na-flux growth of vertically placed single GaN crystals, indicating a significant improvement in thickness uniformity. Numerical optimization reveals that doubling the solution height could improve the uniformity of longitudinal nitrogen concentration adjacent to the seed crystal surfaces. The successful growth of multiple GaN crystals using this method effectively addresses the issue of low crystal growth efficiency and lays a solid foundation for the large-scale production of GaN crystals.