Deep-level trap

Deep-level defects are a generally undesirable type of electronic defect in semiconductors. They are "deep" in the sense of having an energy level near the center of the band gap, making them neither donors nor acceptors. They interfere with more useful types of doping by compensating the dominant charge carrier type, annihilating either free electrons or electron holes depending on which is more prevalent. They also directly interfere with the operation of transistors, light-emitting diodes and other electronic and opto-electronic devices, by offering an intermediate state inside the band gap.

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Common chemical elements that produce deep-level defects in silicon include iron, nickel, copper, gold, and silver. In general, transition metals produce this effect, while light metals such as aluminium do not.