Abstract Formation and transport of Ga-containing intermediates are essential for ammonothermal bulk growth of GaN. In this work, in situ X-ray transmission measurements are established as a tool for monitoring face-selective dissolution of GaN crystals as well as the Ga-concentration in the fluid. The accuracy of concentration determination by X-ray transmission measurements is evaluated and the detection limit for dissolved species is estimated. The detection limit is given both as a gallium concentration and as an attenuation coefficient, thus, it can easily be transferred to other materials of interest. Face-selective ammonothermal etching is investigated for both ammonoacidic and ammonobasic mineralizers. Time- and space-resolved monitoring of the concentration of Ga-containing intermediates is demonstrated using NH4F mineralizer. The results are discussed with respect to the formation of Ga-containing intermediates and mechanisms of mass transport. Based on molecular dynamics simulations, the experimentally observed, unexpectedly low diffusion coefficient for the Ga-transporting species is ascribed at least partially to the diffusion of larger [GaxFy]3x−y aggregates.

中文翻译：

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在 GaN 氨热生长条件下含 Ga 中间体的传输和化学的原位 X 射线监测

摘要 含 Ga 中间体的形成和传输对于 GaN 的氨热体生长至关重要。在这项工作中，原位 X 射线透射测量被确立为监测 GaN 晶体的面选择性溶解以及流体中 Ga 浓度的工具。评估通过 X 射线透射测量确定浓度的准确性，并估计溶解物质的检测限。检测限以镓浓度和衰减系数的形式给出，因此，它可以很容易地转移到其他感兴趣的材料上。研究了针对氨酸和氨碱矿化剂的面选择性氨热蚀刻。使用 NH4F 矿化剂证明了对含 Ga 中间体浓度的时间和空间分辨监测。讨论了关于含 Ga 中间体的形成和质量传输机制的结果。基于分子动力学模拟，实验观察到的、出乎意料的低 Ga 传输物质扩散系数至少部分归因于较大的 [GaxFy]3x-y 聚集体的扩散。