Abstract
Lattice mis-matched (LMM) multilayered structures were grown using metalorganic chemical vapor deposition (MOCVD) at NREL. Energy dispersive x-ray (EDX) spectrometric mapping was conducted on transmission electron microscope (TEM) sample cross-sections of GaAs 1−y P y grades on GaAs substrates, with known layer compositions. The compositions were determined by x-ray diffraction, which serve as standards for EDX. Data were acquired by both TEM spot analysis and 2-D maps in scanning TEM mode. The I P /I As intensity ratio obtained from EDX, plotted against y / (1−y) obtained from XRD shows a linear slope. We seek to parameterize the variations from these standard samples for accurate composition determination of unknown samples [1]. The quantitative method we are developing is based on principle component analysis (PCA) [2, 8]. We anticipate our PCA algorithm will have applications in future growth designs, including heterostructures with multiple quaternary steps, or even continuous grades.
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