Luminescence of doped and undoped bulk crystals of GaN

We have performed measurements of the photoluminescence in undoped (yellow luminescence), Zn-doped and Mg-doped gallium nitride single, bulk crystals. Temperature and pressure induced evolution of the related spectra have been examined. With applying pressure all photoluminescence bands exhibit blue shifts with values similar to the change of GaN band gap with pressure. It supports radiative recombination models with initial states being related to the conduction band or shallow donor states. Yellow luminescence as well as the luminescence in GaN:Zn do not change their position with temperature. In contrast, the temperature evolution of the luminescence in GaN:Mg resembles the changes of the band gap. This fact is consistent with the shallow like character of the acceptor state formed by Mg. Zn- and yellow luminescence -related states have more localized character and exhibit strong electron -lattice coupling effect.