New photosensitive EPR signals in undoped semi-insulating GaAs

Three new EPR signals labelled FR1, FR2 and FR3 have been observed in undoped as grown LEC GaAs. They are well observable only below 10K, their intensities are high and they appear only after optical excitation. Thus the defects involved are electrically active and occur in high concentrations. Tentative models for the three centers are presented. (IAF)