Determination of lattice parameters, strain state and composition in semipolar III-nitrides using high resolution X-ray diffraction
Determination of lattice parameters, strain state and composition in semipolar III-nitrides using high resolution X-ray diffraction
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DOI：
10.1063/1.4834521
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发表时间：
2013-12-07
影响因子：
3.2
通讯作者：
Kneissl, Michael
中科院分区：
文献类型：
--
作者：
Frentrup, Martin;Hatui, Nirupam;Kneissl, Michael
在具有半极性或非极性晶体取向的III族氮化物异质结构中，各向异性晶格和与缓冲层或衬底的热失配导致晶胞的复杂变形，例如，通过晶格的剪切。这使得在六方对称假设下的晶格参数、组成和应变状态的精确确定是不可能的。在这项工作中，我们提出了一个程序，以准确地确定晶格常数，应变状态，和组成的半极性异质结构，使用高分辨率X射线衍射。晶胞畸变的分析表明，四个独立的晶格参数足以描述这种畸变。假设只有很小的偏差，从一个理想的六边形结构，面间距d（hkl）的线性表达式推导。它用于通过加权最小二乘拟合从多个轴上和离轴反射的高分辨率X射线衍射2 Ω扫描确定晶格参数。三元合金的应变和组成，然后通过转换的弹性参数（使用胡克定律）从自然晶体固定的坐标系到一个基于层的系统，给出了面内方向和生长方向进行评估。我们举例说明我们的程序，以（1122）Al（κ）Ga（1-κ）jN外延层的Al含量在整个组成范围内的一个例子。我们分别确定的平面和平面外的应变，并讨论所观察到的各向异性的起源。(C)2013 AIP Publishing LLC.
In group-III-nitride heterostructures with semipolar or nonpolar crystal orientation, anisotropic lattice and thermal mismatch with the buffer or substrate lead to a complex distortion of the unit cells, e.g., by shearing of the lattice. This makes an accurate determination of lattice parameters, composition, and strain state under assumption of the hexagonal symmetry impossible. In this work, we present a procedure to accurately determine the lattice constants, strain state, and composition of semipolar heterostructures using high resolution X-ray diffraction. An analysis of the unit cell distortion shows that four independent lattice parameters are sufficient to describe this distortion. Assuming only small deviations from an ideal hexagonal structure, a linear expression for the interplanar distances d(hkl) is derived. It is used to determine the lattice parameters from high resolution X-ray diffraction 2 upsilon-omega-scans of multiple on-and off-axis reflections via a weighted least-square fit. The strain and composition of ternary alloys are then evaluated by transforming the elastic parameters (using Hooke's law) from the natural crystal-fixed coordinate system to a layer-based system, given by the in-plane directions and the growth direction. We illustrate our procedure taking an example of (1122) Al(kappa)Ga(1-kappa)jN epilayers with Al-contents over the entire composition range. We separately identify the in-plane and out-of-plane strains and discuss origins for the observed anisotropy. (C) 2013 AIP Publishing LLC.