The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in p-type Mg-doped GaN, Al0.2Ga0.8N, and Al0.2Ga0.8N/GaN superlattices, which were homogeneously and modulation (barrier only) doped. The activation energies for the electron injection-induced effect were found to be in the range from 190 to 260 meV, which is close to the thermal ionization energy of the Mg-acceptor. The obtained results are in agreement with the previously proposed model of minority carrier transport enhancement due to charging of Mg-centers in p-(Al)GaN. The activation energy of the electron injection effect observed in Al0.2Ga0.8N is consistent with the deepening of Mg-acceptor level due to the incorporation of Al into GaN lattice. The activation energy in the Al0.2Ga0.8N/GaN superlattice, homogeneously doped with Mg, indicates that the main contribution to the effect comes from the capture of injected electrons by the wells. (C) 2002 Elsevier Science Ltd. All rights reserved.