Post-growth annealing of GaInNAs layers and GaInNAs/GaAs multiple quantum wells studied by photoreflectance spectroscopy

GaInNAs layers almost lattice-matched to a GaAs substrate and GaInNAs/GaAs multiple quantum wells (MQWs) postgrowth annealed at different temperatures are investigated by photoreflectance (PR) spectroscopy. The post-growth annealing leads to an ʹeffectiveʹ blue-shift of the bandgap energy of GaInNAs layers and GaInNAs/GaAs MQWs without a change in the composition of the GaInNAs layer. This phenomenon is associated with the formation of In-N bonds instead of Ga-N bonds, accompanied by the appearance of N atoms in In-rich environments with larger bandgap energies. It is shown that the annealing-induced blue-shift of the bandgap energy, which is usually observed for GaInAsN structures, is associated with a redistribution of the intensity of the optical features related to the different energy gaps possible for this quaternary material. The findings are a manifestation of the metastability of optical properties for GaInNAs-based structures.