Spin Transport in Si and Ge
The spin injection and detection limitations posed by conductivity and lifetime mismatch between semiconductors and ferromagnetic (FM) metals has been variously solved by lifting the constraints of ohmic transport with the insertion of a tunnel barrier or the use of ferromagnetic semiconductors. There are several techniques for generating hot electrons for injection from a metal into a semiconductor. Spin-polarized electrons in silicon (Si) were first studied decades ago using resonance between Zeeman-split levels in a large magnetic field. Demonstrations of electrically injected spin accumulation in nonmagnetic materials are considered reliable when measured in a non-local four-terminal geometry. When performed correctly, the experiment electrically measures the decay of spin polarization in the nonmagnetic bulk material between the injection and detection regions. There has been significant progress in using ballistic hot electron spin injection and detection techniques for spin transport studies in Si and germanium.