ELECTRICAL-PROPERTIES OF NICKEL IN SILICON

Electrical activity and energy levels as well as diffusion properties of nickel in silicon have not yet been reliably established. In this paper, we investigated the diffusion and the electrical properties of nickel in silicon to confirm that nickel is electrically active and introduces one acceptor and one donor level by combined measurements of Hall coefficient and DLTS, and measurements of the distribution of electrically active nickel in various silicon diodes by DLTS. The former experiments show that both n- and p-type silicon are compensated by nickel and that nickel introduces an acceptor level of E(c) -0.47 +/- 0.04 eV and a donor level of E(v) + 0.18 +/- 0.02 eV. The concentrations of these two levels are almost identical over the diffusion temperatures from about 800 to 1100-degrees-C, indicating that these donor and acceptor levels are due to different charge states of the same nickel center. In the distribution measurements of electrically active nickel in silicon diodes, we inspected how nickel can be observed by DLTS. It was found that the nickel diffusion into p-n junction is rather complicated, the distribution profiles of nickel in the vicinity of the p-n junction being markedly influenced by an additional heating at elevated temperatures after the nickel diffusion. This gives evidence that the difference in silicon devices used in various studies could give rise to different results.