Irradiation by the beam of the scanning electron microscope is shown to induce a systematic decay of the cathodoluminescence intensity in gallium nitride semiconductor doped with carbon. This decay is accompanied by increased electronic carrier diffusion length, indicating that electron irradiation results in the increase of carrier lifetime. Temperature-dependent cathodoluminescence measurements yielded activation energy for irradiation-induced effect of 210 meV. This observation is consistent with trapping of non-equilibrium electrons on deep, non-ionized carbon levels. (c) 2006 Elsevier B.V. All rights reserved.