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.