Dielectric function and bowing parameters of InGaN alloys

Ga‐rich (0001)‐oriented InxGa1−xN alloys grown by molecular beam epitaxy or metal‐organic vapour phase epitaxy on GaN/sapphire templates were investigated by spectroscopic ellipsometry at room temperature. The analysis of the extracted dielectric function yielded the characteristic transition energies, i.e., for the band gaps and the high‐energy critical points (van Hove singularities). Accounting for strain by using the k · p formalism, a band‐gap bowing parameter of 1.65 ± 0.07 eV for strain‐free material was deduced. It is consistent with the ab initio calculated band‐gap‐dependence for uniform (not clustered) InGaN alloys. The bowing parameters for the high‐energy inter‐band transitions were found to be close to ∼1 eV.