Deep centers in Si-dopedn-GaNlayers grown by reactive molecular beam epitaxy have been studied by deep-level transient spectroscopy as a function of growth conditions. Si-doped GaN samples grown on a Si-dopedn+-GaNcontact layer at 800 °C show a dominant trapC1with activation energyET=0.44 eVand capture cross-section&sgr;T=1.3×10−15 cm−2,while samples grown at 750 °C on an undoped semi-insulating GaN buffer show prominent trapsD1andE1,withET=0.20 eVand&sgr;T=8.4×10−17 cm2,andET=0.21 eVand&sgr;T=1.6×10−14 cm2,respectively. TrapE1is believed to be related to a N-vacancy defect, since the Arrhenius signature forE1is very similar to the previously reported trapE,which is produced by 1-MeV electron irradiation in GaN materials grown by both metalorganic chemical-vapor deposition and hydride vapor-phase epitaxy. ©1998 American Institute of Physics.