Optical characterization of AlxGa1-xN alloys (x < 0.7) grown on sapphire or silicon

The optical properties of Al x Ga 1-x N samples (x < 0.7) have been studied by photoluminescence (PL) and reflectivity in the 10-300 K temperature range. Various physical properties have been studied as a function of composition, such as Stokes shift, alloy broadening, exciton localization, and Huang-Rhys factor. Up to x 0.3, a band gap bowing factor of ∼0.9 eV accounts for the variation of PL and reflectivity energies. At higher compositions, luminescence energies deepen with regard to this behaviour. This is interpreted as a consequence of the Γ 9 -Γ 7 crossover of the valence band maxima. This is confirmed by the linear polarization of the luminescence studied under oblique observation.