Modeling spin transport in electrostatically-gated lateral-channel silicon devices: Role of interfacial spin relaxation

Using a two-dimensional finite-differences scheme to model spin transport in silicon devices with lateral geometry, we simulate the effects of spin relaxation at interfacial boundaries, i.e., the exposed top surface and at an electrostatically-controlled backgate with a SiO₂ dielectric. These gate-voltage-dependent simulations are compared to previous experimental results and show that strong spin relaxation, due to extrinsic effects, yields a Si_/SiO2 interfacial spin lifetime of ≈1ns, orders of magnitude lower than lifetimes in the bulk Si. Relaxation at the top surface plays no substantial role. Hall effect measurements on ballistically injected electrons gated in the transport channel yield the carrier mobility directly and suggest that this reduction in spin lifetime is only partially due to enhanced interfacial momentum scattering, which induces random spin flips as in the Elliott effect. Therefore, other extrinsic mechanisms, such as those caused by paramagnetic defects should also be considered in order to explain the dramatic enhancement in spin relaxation at the gate interface over bulk values.