Local Structure Properties of Ga1-xAlxN Epitaxial Layer

The strained-tetrahedron model is used to analyze the wurzite structure of epitaxial GaAlN thin films on a sapphire substrate. Site occupation preference (SOP) coefficients and first two shell inter-ion distances are calculated in the ideal wurzite structure approximation. The coefficient values W1=0, W2=1.86, and W3=1, indicate a strong deviation from a random distribution with preference of Ga-N to Al-N pairs. This suggests that GaAlN thin films could be less homogeneous and more difficult to grow beyond 50% AlN. Also the far-infrared GaAlN phonon spectra should exhibit only four strong lines instead of eight.