Carrier capture at amphoteric deep level defects in silicon

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Abstract
Thermodynamic concepts relating to carrier capture and emission processes are reviewed and revised for interactions at deep-level defects where lattice (Jahn-Teller) interactions are important. Criteria for the applicability of concepts like atomic degeneracy ratios, which are used to relating emission and capture rates, are established. Mechanisms for capture of both electrons and holes at the Au defect and some other centres which are similarly bonded are discussed. It is suggested that the mechanism of electron capture at Au, Pt, Pd, Rh and A centre defects is a smooth relaxation process akin to multiphonon tunnelling emission, possibly involving motion of the chemical impurity, and giving an 'energy gap' dependence for the capture cross section on the thermal ionisation energy. Hole capture involves a localisation of the hole on the reconstructed bonds adjacent to the chemical defect prior to recombination with the donor electron.