The grasshopper effect in the diamond lattice

Abstract

The earlier notion of point defects in diamond-like crystals has by now undergone changes. The models of isolated vacancies and interstitials often prove inadequate for the interpretation of radiation effects. Theoretical and experimental results reveal new metastable configurations of point defects. A thorough investigation was carried out of the metastable configuration of point defects in silicon by means of the quantum-chemical simulation method. The cluster computation was carried out by an US-1020 computer. The accuracy of energy estimation is 0.1 eV. The cluster model was selected with regard to solving dynamic problems and constructing the potential pattern. A composite (quantum-classical) model of the diamond lattice cluster was elaborated. Two inner coordination spheres (17 atoms) were described quantum-mechanically in the two-centre approximation. Two external spheres (91 atoms in the cluster altogether) were described by means of classical potentials of the Morse type. The recovery of the defect configuration in the vicinity of B results in a rightward displacement of atom B and in the appearance of analogous defect configurations in the vicinity of B. There occurs a "jump-over" of the area with turned-about bonds, resembling the jump of a grasshopper ("grasshopper effect"). The grasshopper effect points to another possibility of migration of defect configurations in the diamond lattice. The migration of this kind is not longrange and cannot be regarded as ordinary traditional point defect. Nevertheless, this effect can be used for the interpretation of radiation-enhanced diffusion, migration of sub-threshold defects, and certain phenomena observed at Si implantation.