Excitonic emissions under high excitation of hexagonal GaN single crystal grown by sublimation method

Excitonic emission lines from hexagonal-structured GaN single crystals grown by the sublimation method have been studied at 4.2 K. A dominant I-2 line at 3.4706 eV, which is probably ascribed to the radiative recombination of an exciton bound to a neutral donor, has a linewidth of 2.1 meV under low excitation. Fine structures around 3.475 eV and 3.479 eV appear with increasing excitation power density. These positions correspond to those of A free exciton and B-free exciton in strain-relaxed GaN crystal, respectively. A new line at 3.454 eV can be observed above 270 kW/cm(2) and gradually shifts towards the low-energy side with a further increase in excitation power density. It is suggested that the origin of this line is due to the inelastic exciton-exciton interaction. The emission related to dense exciton gas was observed in the excitonic luminescence from bulk GaN for the first time.