Two competing recombination mechanisms of stimulated emission in the vicini
ty of 145 K have been directly observed in the temperature dependence of th
e optical emission spectra for high-quality, unintentionally doped gallium
nitride. Our analysis of the spectra indicates that exciton-exciton scatter
ing is responsible for stimulated emission below 145 K, while at higher tem
peratures an electron-hole plasma becomes the dominant mechanism. (C) 2000
American Institute of Physics. [S0003- 6951(00)02051-9].