Anion antisite defects are the first convincingly identified intrinsic lattice defect in GaAs. Photo-EPR allowed to determine the energy levels of this double donor, with the single donor level being midgap. This level appears to be very similar to the technologically important “EL2” center in GaAs. However, various evidence indicates that EL2 is not due to ideal, undistorted antisite defects.
Fermi level pinning at Schottky contacts on GaAs has been ascribed to intrinsic lattice defects. Antisite defects are a likely candidate for this process.
Finally, the microscopic identity of the “DX” center in AlGaAs will be discussed. This defect has been generally identified with a complex of a donor atom and an unknown partner. A number of recent experimental observations indicate that this defect might rather be due to isolated donors, which get deep levels because of the change of bandstructure in the alloy system.