Influence of the type of carrier on ferromagnetism in Si semiconductor implanted with Cu ions
Silicon semiconductor samples implanted with Cu ions and samples co-implanted with Cu- and N-ions were prepared by MEVVA and the Kaufman technique. None of the samples showed evidence of secondary phases. The initially n-type Si matrix, when implanted with Cu ions, changed to a p-type semiconductor, and the Cu ions existed as local Cu2+ cations in the p-type environment. As a result, none of the Cu-implanted samples were ferromagnetic at room temperature. The co-implanted samples, on the other hand, showed room-temperature ferromagnetism because the introduction of N ions made the carrier type change from p-type to n-type which is favorable for the appearance of Cu2+. The first principle calculations were applied to understand the experimental phenomena. The formation energy reduced by the implanted N ions, and decreased effectively with the ratio of N to Cu ions increasing. The density of states and spin density of states indicated that hybridization of s, p and d electrons induced the ferromagnetic at 0 K. Based on the electron density and the electron spin density, we proposed a exchange interaction between of the Cu2+-N-(N4+)-Cu2+ ions mediated to explain the ferromagnetism.