Determination of indium content of GaAs/(In,Ga)As/(GaAs) core-shell(-shell) nanowires by x-ray diffraction and nano x-ray fluorescence
Determination of indium content of GaAs/(In,Ga)As/(GaAs) core-shell(-shell) nanowires by x-ray diffraction and nano x-ray fluorescence
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DOI：
10.1103/physrevmaterials.2.014604
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发表时间：
2018-01-19
影响因子：
3.4
通讯作者：
Pietsch, U.
中科院分区：
文献类型：
--
作者：
Al Hassan, Ali;Lewis, R. B.;Pietsch, U.
提出了两种利用同步辐射研究GaAs/（In，Ga）As/（GaAs）核壳（-壳）纳米线异质结构中In含量的互补方法。我们的方法的主要优点是纳米线的特征在于它们的生长配置，即，垂直地立在基板上。首先，我们确定的平均含量的（In，Ga）作为壳层的高分辨率X射线衍射（XRD）从NW系综。特别地，我们通过测量和分析衍射矢量平行和垂直于生长轴的两个反射，分别解开In含量和壳层厚度对XRD的影响。其次，我们研究了在个别纳米线内的纳米X射线荧光分布。用50 nm宽的入射纳米束扫描平行于衬底表面的NW（111）基面和{10-1}侧壁面。我们调查了三个样品具有不同的名义含量的（In，Ga）As壳。在所有样品中，通过XRD测定的壳的平均In含量与标称值良好一致。对于15%的标称In含量，In分布在所有六个侧壁刻面之间相当均匀。相比之下，在名义上In含量为25%的NW中，同一NW的不同侧壁面表现出不同的In含量。这种效应是由于在分子束外延生长过程中的阴影。同时，In分布在沿着NW轴方向上仍相当均匀.在具有60%标称In含量且没有外部GaAs壳的NW中，In含量在不同侧壁刻面之间和沿着NW轴两者之间显著变化。这种波动是由形成的（In，Ga）As土丘，同时生长的薄（In，Ga）As壳解释。这里提出的方法也可以应用到其他核-壳纳米线与三元壳，并铺平了道路，以相关的NW结构与功能特性，取决于作为生长配置的纳米线。
We present two complementary approaches to investigate the In content in GaAs/(In, Ga)As/(GaAs) core-shell(-shell) nanowire (NW) heterostructures using synchrotron radiation. The key advantage of our methodology is that NWs are characterized in their as-grown configuration, i.e., perpendicularly standing on a substrate. First, we determine the mean In content of the (In, Ga) As shell by high-resolution x-ray diffraction (XRD) from NW ensembles. In particular, we disentangle the influence of In content and shell thickness on XRD by measuring and analyzing two reflections with diffraction vector parallel and perpendicular to the growth axis, respectively. Second, we study the In distribution within individual NWs by nano x-ray fluorescence. Both the NW(111) basal plane, that is parallel to the surface of the substrate, and the {10-1} sidewall plane were scanned with an incident nanobeam of 50 nm width. We investigate three samples with different nominal In content of the (In, Ga) As shell. In all samples, the average In content of the shell determined by XRD is in good agreement with the nominal value. For a nominal In content of 15%, the In distribution is fairly uniform between all six sidewall facets. In contrast, in NWs with nominally 25% In content, different sidewall facets of the same NW exhibit different In contents. This effect is attributed to shadowing during growth by molecular beam epitaxy. At the same time, along the NW axis the In distribution is still fairly homogeneous. In NWs with 60% nominal In content and no outer GaAs shell, the In content varies significantly both between different sidewall facets and along the NW axis. This fluctuation is explained by the formation of (In, Ga) As mounds that grow simultaneously with a thinner (In, Ga) As shell. The methodology presented here may be applied also to other core-shell NWs with a ternary shell and paves the way to correlating NW structure with functional properties that depend on the as-grown configuration of the NWs.