Dynamics of excited states in GaN

We report a review of the optical properties of GaN epilayers. Photoluminescence, time-resolved and photoluminescence excitation measurements on hexagonal and cubic GaN heterostructures from the band edge region down to the near infrared spectral region provide information about excitonic properties as well as the influence of point and extended defects. Spatially resolved Raman-scattering and photoluminescence experiments allow to analyze the crystal structure, layer orientation and strain contribution to the lattice properties. Luminescence measurements at high excitation densities will be presented giving information about optical gain mechanisms.