Alloy distribution and compositional metrology of epitaxial ScAlN by atom probe tomography

The properties of ScAlN layers grown by molecular beam epitaxy have been carefully studied using atom probe tomography (APT) and complementary techniques. The measured III-site fraction within the ScxAl1-xN layer is x=0.16 +/- 0.02, in good agreement with the values determined by x-ray photoelectron spectroscopy (XPS, x=0.14) and secondary ion mass spectrometry (SIMS, x=0.14). The frequency distribution analysis indicates that the compound behaves as a random alloy. A significant amount of oxygen, around 0.2% in site fraction, is found within the ScAlN layer as a randomly distributed impurity. The alloy composition measurement in terms of Sc fraction is rather independent of the surface electric field, which excludes compositional inaccuracies for the experimental parameters used in the APT analysis.