Abstract
Photoluminescence intensities, energies, and band shapes of GaN needle crystals are studied as a function of temperature in the range of 4.2–300 K. An emission at 3.472 eV due to a bound exciton localized at a neutral donor site (so-called I2 line) dominates the spectrum at 4.2 K. A donor-acceptor pair recombination band is observed near 3.27 eV. The I2 line quenches with an activation energy of 10±1 meV in the temperature range of 30–80 K, and is not observed at higher temperatures. The activation energy corresponds to the localization energy of the I2-line exciton. The donor-acceptor band quenches at temperatures above 150 K with an activation energy of 160±20 meV, which corresponds to the acceptor binding energy.