Spin injection in a semiconductor through a space-charge layer

•Spin injection from a space charge layer in a semiconductor is shown.•Charge neutrality fixes the value of possible maximum spin current.•Bulk spin current is not enhanced for the presence of a space-charge layer.•Spin current is largest at maximum spin polarization of the injected carriers.

The electron spin properties provided by semiconductors are of immense interest because of their potential for future spin-driven microelectronic devices. Modern charge-based electronics is dominated by silicon, and understanding the details of spin propagation in silicon structures is key for novel spin-based device applications. We performed simulations on electron spin transport in an n-doped silicon bar with spin-dependent conductivity. Special attention is paid to the investigation of a possible spin injection enhancement through an interface space-charge layer. We found substantial spin transport differences between the spin injection behavior through an accumulation and a depletion layer. However, in both cases the spin current density can not be significantly higher than the spin current density at charge neutrality. Thus, the maximum spin current in the bulk is determined by its value at the charge neutrality condition - provided the spin polarization at the interface as well as the charge current are fixed.