Metastable Zn-related centres in silicon

Photo-EPR evidence has yielded metastable negative-U properties for Zn-related double accepters in silicon. The spectral distributions of photoionization cross sections for D- and D-- states of the orthorhombic Zn-related centre as well as the monoclinic CuZn and trigonal CrZn pairs are discussed. The data analysis in terms of a model for the deep defect tunnelling between the D2d (D0 state), C2V (paramagnetic D- state) and C3V (D-- state) interstitial lattice positions indicates that the (ZniVSi)- orthorhombic centre should spontaneously decay into the (ZniVSi)0 and (ZniVSi)-- states, as is consistent with the negative-U reaction: 2D- to D--+D0, whereas the D- state of the CuZn and CrZn pairs is more stable because of the energy barriers between the lattice positions of the centre charge states. A photo-EPR Study Of reactions involving the transfer of holes via the valence band between the orthorhombic Zn-related centres and CuZn pairs is also analysed. All aspects of the negative-U properties for the orthorhombic Zn-related centre can be confirmed by monitoring the intensity of the EPR signals for Zn-related defects of both types.

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