METASTABLE ZN-RELATED CENTERS 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 D-2d (D-0 state), C-2V (paramagnetic D- state) and C-3V (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(-) --> D-- + D-0, 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.