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We describe how the electrical characteristics (energy level in the gap, electron capture cross section) a defect has in a bulk material are modified when this defect is placed in the well or the barrier of a superlattice. The relations between these characteristics we deduce are verified in GaAs-GaAlAs superlattices using electron irradiation induced defects as test. The implications of these considerations to the characterization of deep levels in superlattices as well as of the superlattices themselves are discussed.

In Si doped GaAlAs layers and two different types of GaAs-AlAs superlattices grown by molecular beam epitaxy we detect using deep level transient spectroscopy the DX center. The energetical location of the DX level is compared to the band structures of these superlattices allowing us to conclude that the DX state is linked to the L band.