We report on carbon doping of cubic GaN by CBr(4) using plasma-assisted molecular beam epitaxy. Cubic GaN:C samples were doped at different CBr(4) beam equivalent pressures between 2 x 10(-9) and 6 x 10(-6) mbar. The incorporated carbon concentration of up to 1 x 10(20) cm(-3) was achieved in c-GaN:C as measured by secondary ion mass spectroscopy. The net donor/acceptor concentration was obtained by evaluation of capacitance-voltage data. Capacitance-voltage measurements on nominally undoped cubic GaN showed n-type conductivity. With an increase in CBr(4) flux the conductivity type changed to p-type and for highest CBr(4) flux an acceptor surplus of 1 x 10(19) cm(-3) was obtained. The electrical properties of the c-GaN:C layers were investigated by current-voltage measurements and a decrease in the serial conductance by two orders of magnitude was demonstrated in c-GaN:C. A blue shift of the 2 K donor-acceptor pair luminescence with an increase in carbon concentration was obtained. (C) 2011 Published by Elsevier B.V.