Spin injection into Silicon using Al$_2$O$_3$, SiO$_2$ and MgO tunnel barriers

We recently demonstrated injection of spin-polarized electrons from an Fe film into Si.\footnote{B. T. Jonker et al., Nature Phys. 3, 542 (2007), O.M.J. van 't Erve et al., App. Phys. Lett. 91, 212109, (2007)} The tunnel barrier is the key component in achieving a large spin accumulation in the semiconductor. Here we will compare three different tunnel barriers, Al$_2$O$_3$, SiO$_2$ and MgO, on highly doped Si using three terminal Hanle measurements. Hanle measurements give insight in the spin-accumulation directly underneath the spin injecting contact. We will compare temperature dependence and bias dependence as well as the tunnel barrier properties such as density of interface states based on I-V and C-V measurements. We will compare spin-injection properties, such as spin lifetimes and spin injection efficiency with the oxide/Silicon interface. A spin lifetime of 120ps was obtained for 3e19 n-doped Silicon for both the Al$_2$O$_3$ and SiO$_2$ tunnel barrier, indicating that the spin accumulation occurs in the Si rather than in surface states. Support by ONR.