Direct determination of Al content in molecular-beam epitaxially grown AlxGa1–xAs (0<=x<=1) by nuclear resonant reaction analysis and x-ray rocking curve techniques

Abstract

The techniques of nuclear resonant reaction analysis (NRRA) using 27Al(p,gamma)28Si and x-ray rocking curve (XRC) based on double-crystal diffractometry have been utilized to determine directly the Al concentration and its depth distribution in molecular-beam epitaxially (MBE) grown AlxGa1–xAs/GaAs heterojunctions. Combination of these two methods has revealed a linear relationship between the Al mole fraction and the lattice strain. This can eliminate the need for assuming that Vegard's law holds and that extrapolated elastic coefficients are accurate. The result supports that both of these two techniques provide an accurate determination of the absolute Al content and crystalline quality in AlxGa1–xAs/GaAs throughout the entire composition range (0<=x<=1) as well as profiling the Al distribution. In addition, significant depth fluctuations in the Al mole fraction in some samples have been probed by the NRRA technique as well as by the XRC. The result suggests that a reliable and accurate measurement must be undertaken to ensure the control of the required Al distribution, which is necessary for the high performance of many devices.

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