Transition energies and Stokes shift analysis for In-rich InGaN alloys

The absorption and emission properties of In-rich InGaN alloys were studied by spectroscopic ellipsometry and photoluminescence spectroscopy, respectively. Films grown on a GaN buffer layer show a much sharper increase of the imaginary part of the dielectric function around the band gap and a slightly reduced Stokes shift compared to layers grown directly on AlN buffers. It is attributed to a reduced electron concentration and improved structural quality of the films. By fitting the third derivatives of the dielectric functions up to 9.5 eV we determine for the first time the compositional dependences (bowing parameters) of the transition energies for at least four critical points of the band structure.