Rich chemistry of copper in crystalline silicon

The interstitial copper ion (Cu-i(+)) is a very fast-diffusing impurity in Si. While the isolated interstitial is a shallow donor, it reacts with impu rities and defects and these reactions affect the electrical properties of the material. Copper passivates shallow acceptors, forms pairs with various impurities, including itself, and precipitates at defects. Some Cu precipi tates are strong electron-hole recombination centers. In this paper, inters titial and substitutional copper, copper-acceptor pairs, and the precipitat ion of copper at a model nanodefect, the ring hexavacancy, are studied in c lusters at the ab initio Hartree-Fock level. The chemistry of copper in Si is not as simple as commonly believed, even in the case of Cu-i(+). The int erstitial ion is not in the 3d(10)4sp(0) configuration as often assumed, bu t transfers some electrons into the 4sp shell, which ultimately is responsi ble for the various covalent interactions between copper and its host cryst al. In addition to energy-optimized configurations and binding energies, a number of details of the chemical interactions shed light on the behavior o f copper in silicon. [S0163-1829(99)00232-5].