The dissociation energy and the charge state of a copper-pair center in silicon

Thermal dissociation of Cu pairs was studied in p-type silicon. The dissociation energy of the Cu pair was found to be 1.02±0.07 eV, twice as high as the binding energy of a Coulombically bound donor-acceptor pair placed on nearest neighbor 〈111〉 sites. This implies that the pair is either covalently bonded, or it consists of an ionically bonded doubly negatively charged acceptor and a singly charged donor. To distinguish between these two models, the dependence of the hole emission rate on the electric field in the depletion region was studied. The absence of the Pool-Frenkel emission enhancement ruled out the acceptor nature of the center and the purely ionic type of bonding. On the other hand, the polarization potential describing emission from a neutral impurity gave a satisfactory fit to the experimental data. It is concluded that the Cu pair is a donor with either covalent or mixed type of bonding.