  Individual dislocations in an ultra-pure GaAs epilayer are investigated with
spatially and spectrally resolved photoluminescence imaging at 5~K. We find
that some dislocations act as strong non-radiative recombination centers, while
others are efficient radiative recombination centers. We characterize
luminescence bands in GaAs due to dislocations, stacking faults, and pairs of
stacking faults. These results indicate that low-temperature,
spatially-resolved photoluminescence imaging can be a powerful tool for
identifying luminescence bands of extended defects. This mapping could then be
used to identify extended defects in other GaAs samples solely based on
low-temperature photoluminescence spectra.
