Carrier trapping and recombination at carbon defects in bulk GaN crystals grown by HVPE

We investigate the impact of carbon defects on carrier trapping and recombination processes in high-quality GaN crystals using transient absorption spectroscopy (TAS). The different wavelengths for probing carrier dynamics enable discrimination of electron- and hole-capture processes by carbon acceptors (C-N), and two charge states (-1 and 0) of the C-N are demonstrated from TAS by tuning the pump fluence. The hole-capture coefficients for the C-N(-) and C-N(0) states are at least ten times larger than that for Fe centers. On the other hand, electrons can also recombine efficiently with holes at the 0/+ level of the C-N defect. The resulting carrier trapping on carbon in GaN would mediate carrier recombination and significantly reduce the efficiency of optoelectronic devices even for a low defect concentration (similar to 10(15)cm(-3)).