Energy band-gap bowing parameter in an Al<i>x</i>Ga1−<i>x</i> N alloy

Optical measurements are performed near the fundamental absorption edge for single-crystal AlxGa1−x N epitaxial layers in the composition range of 0≤x≤0.4. The dependence of the energy band gap on composition is found to deviate downwards from linearity, the bowing parameter being b=1.0±0.3 eV. The origin of the large bowing is discussed in terms of the pseudopotential of Al and Ga based on the pseudopotential of the Heine–Abarenkov type. With increasing x the absorption edges broaden, which is attributed to the increase of the compositional nonuniformity.