Figure 1 . Low-temperature photoluminescence spectra of HVPE GaN at various excitation densities. Figure 2 . Figure 3 . Peak positions of HE luminescences as a function of temperature.
Symbols represent the experimental data.
Circled symbols mark the energy of the maximum HE-luminescence intensity, full circles give the energy of the maximum of the optical gain at the respective temperature. Solid lines are fits, cf. Figure 4 . Gain spectra of GaN at three different temperatures.