Cobalt-Al₂O₃-silicon tunnel contacts for electrical spin injection into silicon

The resistance of Co–Al₂O₃–Si tunnel contacts for electrical spin injection from a ferromagnet into silicon is investigated. The contacts form a substantial Schottky barrier, 0.7 eV, which plays a dominant role in the electronic transport. On Si with a low doping concentration (∼10¹⁵ cm⁻³), the contact resistance is affected by the Al₂O₃ tunnel barrier only in the forward bias. In the reverse bias (the spin injection condition), the Schottky barrier results in a very high contact resistance, ∼ 10² Ω m². While the contact resistance is improved to ∼ 10⁻² Ω m² using Si with a high doping concentration ( ∼ 5×10¹⁹ cm⁻³), it is still about five to six orders of magnitude higher than the value needed for resistance matching to silicon.