Scientists at the Naval Research Laboratory (NRL) have efficiently injected a current of spin-polarized electrons from a ferromagnetic metal contact into silicon, producing a large electron spin polarization in the silicon. Silicon is by far the most widely used semiconductor in the device industry, and is the basis for modern electronics. This demonstration by NRL scientists is a key enabling step for developing devices which rely on electron spin rather than electron charge, a field known as semiconductor spintronics, and is expected to provide higher performance with lower power consumption and heat dissipation. The complete findings of this study titled, âElectrical spin injection into silicon from a ferromagnetic metal/tunnel barrier contactâ are published in the August 2007 issue of Nature Physics.
This very recent work by NRL scientists demonstrates that high electron spin polarizations can be achieved in silicon by electrical injection of current from a ferromagnetic metal, such as an iron film. This contact is applied by vacuum deposition after a simple wet chemical cleaning of the silicon wafer. Their approach injects spin-polarized electrons near the silicon conduction band edge with near unity conversion efficiency and low bias voltages (~ 2 eV) compatible with CMOS technology. By analyzing the weak electroluminescence generated in the silicon, the NRL research team determined a lower bound for the electron spin polarization of 30%. For comparison, the spin polarization of the electrons in common magnetic metals such as permalloy or iron is ~ 40- 45%. The realization of efficient electrical injection and significant spin polarization using a simple magnetic tunnel barrier compatible with "back-end" silicon processing should greatly facilitate development of silicon-based spintronic devices.