Ju Guangxu, Xu Dongwei, Thompson Carol, Highland Matthew J, Eastman Jeffrey A, Walkosz Weronika, Zapol Peter, Stephenson G Brian
Materials Science Division, Argonne National Laboratory, Lemont, IL, USA.
Lumileds Lighting Co., San Jose, CA, USA.
Nat Commun. 2021 Mar 19;12(1):1721. doi: 10.1038/s41467-021-21927-5.
The stacking sequence of hexagonal close-packed and related crystals typically results in steps on vicinal {0001} surfaces that have alternating A and B structures with different growth kinetics. However, because it is difficult to experimentally identify which step has the A or B structure, it has not been possible to determine which has faster adatom attachment kinetics. Here we show that in situ microbeam surface X-ray scattering can determine whether A or B steps have faster kinetics under specific growth conditions. We demonstrate this for organo-metallic vapor phase epitaxy of (0001) GaN. X-ray measurements performed during growth find that the average width of terraces above A steps increases with growth rate, indicating that attachment rate constants are higher for A steps, in contrast to most predictions. Our results have direct implications for understanding the atomic-scale mechanisms of GaN growth and can be applied to a wide variety of related crystals.
六方密堆积及相关晶体的堆垛顺序通常会在近邻的{0001}表面上形成台阶，这些台阶具有交替的A和B结构，且生长动力学不同。然而，由于很难通过实验确定哪个台阶具有A或B结构，因此无法确定哪个具有更快的吸附原子附着动力学。在此，我们表明原位微束表面X射线散射可以确定在特定生长条件下A或B台阶哪个具有更快的动力学。我们通过（0001）GaN的有机金属气相外延来证明这一点。生长过程中进行的X射线测量发现，A台阶上方台面的平均宽度随生长速率增加，这表明与大多数预测相反，A台阶的附着速率常数更高。我们的结果对于理解GaN生长的原子尺度机制具有直接意义，并且可以应用于多种相关晶体。
