Abstract
Deep-level photoluminescence (PL) at room temperature has been used to determine the two-dimensional distribution of the dominant midgap donor EL2 in undoped semi-insulating GaAs crystals grown by the liquid encapsulated Czochralski method. Various fourfold symmetric patterns have been observed in PL maps of the EL2-related band or conventional (100) wafers. The patterns correlate closely with the EL2 distributions reported previously using optical absorption spectroscopy, but not with the patterns for the band-edge PL. A PL mapping under a high spatial resolution reveals a cellular structure in a highly dislocated area in the central part of the wafers.