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首页> 外文期刊>Nanotechnology >Self-assembled growth of GaN nanowires on amorphous AlxOy: from nucleation to the formation of dense nanowire ensembles
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Self-assembled growth of GaN nanowires on amorphous AlxOy: from nucleation to the formation of dense nanowire ensembles

机译：非晶AlxOy上GaN纳米线的自组装生长：从成核到致密纳米线集合体的形成

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摘要

We present a comprehensive description of the self-assembled nucleation and growth of GaN nanowires (NWs) by plasma-assisted molecular beam epitaxy on amorphous AlxOy buffers (a-AlxOy) prepared by atomic layer deposition. The results are compared with those obtained on nitridated Si(111). Using line-of-sight quadrupole mass spectrometry, we analyze in situ the incorporation of Ga starting from the incubation and nucleation stages till the formation of the final nanowire ensemble and observe qualitatively the same time dependence for the two types of substrates. However, on a-AlxOy the incubation time is shorter and the nucleation faster than on nitridated Si. Moreover, on a-AlxOy we observe a novel effect of decrease in incorporated Ga flux for long growth durations which we explain by coalescence of NWs leading to reduction of the GaN surface area where Ga may reside. Dedicated samples are used to analyze the evolution of surface morphology. In particular, no GaN nuclei are detected when growth is interrupted during the incubation stage. Moreover, for a-AlxOy, the same shape transition from spherical cap-shaped GaN crystallites to the NW-like geometry is found as it is known for nitridated Si. However, while the critical radius for this transition is only slightly larger for a-AlxOy than for nitridated Si, the critical height is more than six times larger for a-AlxOy. Finally, we observe that in fully developed NW ensembles, the substrate no longer influences growth kinetics and the same N-limited axial growth rate is measured on both substrates. We conclude that the same nucleation and growth processes take place on a-AlxOy as on nitridated Si and that these processes are of a general nature. Quantitatively, nucleation proceeds somewhat differently, which indicates the influence of the substrate, but once shadowing limits growth processes to the upper part of the NW ensemble, they are not affected anymore by the type of substrate.
机译：我们对通过原子层沉积制备的非晶AlxOy缓冲液（a-AlxOy）上的等离子辅助分子束外延生长对GaN纳米线（NWs）的自组装成核和生长的全面描述。将结果与在氮化Si（111）上获得的结果进行比较。使用视线四极杆质谱，我们从孵育和成核阶段开始，直到最终的纳米线整体形成，就地分析了Ga的掺入，并定性地观察了两种类型底物的时间依赖性。但是，与氮化硅相比，在a-AlxOy上的孵育时间更短且成核速度更快。此外，在a-AlxOy上，我们观察到了在长生长时间内降低掺入的Ga的通量的新效果，这可以通过NW的聚结来解释，这导致Ga可能驻留的GaN表面积减少。专用样品用于分析表面形态的演变。特别是，在孵育阶段中止生长时，未检测到GaN核。而且，对于α-AlxOy，发现了与氮化硅一样的从球形帽状GaN微晶到类似NW几何形状的相同形状过渡。然而，尽管对于a-AlxOy而言，该转变的临界半径仅比氮化Si稍大，但对于a-AlxOy而言，临界高度却是其六倍以上。最后，我们观察到在完全开发的NW乐团中，基板不再影响生长动力学，并且在两个基板上都测量到相同的N极限轴向生长速率。我们得出的结论是，在a-AlxOy上发生与在氮化Si上相同的成核和生长过程，并且这些过程具有一般性。在数量上，成核的过程有所不同，这表明了基质的影响，但是一旦阴影将生长过程限制在西北集合体的上部，它们就不再受到基质类型的影响。

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