Current-voltage, Capacitance - voltage and Deep level transient spectroscopic (DLTS) studies have been carried out on the high energy carbon ions irradiated (1x10(11) and 1x10(12)) Au/n-GaAs SBDs. The barrier height of the irradiated diodes is decreased whereas the ideality factor is increased due to irradiation-induced defects. After the irradiation, the carrier concentration of the diodes decreases due to irradiation induced defects trapping of free electrons in the depletion region. An electronic energy level EL3 has been observed for both un-irradiated and irradiated diodes. The defect level is due to carbon related complex defect associated with arsenic vacancy.