Correlation between in-plane strain and optical polarization of Si-doped AlGaN epitaxial layers as a function of Al content and Si concentration

We have investigated the relationship between in-plane strain and optical polarization in AlGaN epitaxial layers as a function of Al content and of Si concentration. Al content and in-plane strain were measured by reciprocal space mapping using a simple relationship from the tensor of elastic moduli. The change of valence band energy separation based on the measured in-plane strain was in good agreement with the change of polarization degree as a function of Al content. The dependence of polarization degree on Si concentration was also explained by the change of in-plane strain, and polarization switching occurred around the Al content and strain as calculated by the k · p approach with the cubic approximation.