Spin extraction from a semiconductor through a space-charge layer and critical current density

Simulations are carried out to study the extraction of spin-polarized electrons at a nonmagnetic semiconductor/ferromagnetic semiconductor junction in the presence of a space-charge layer. A spin blockade which limits the current flow in the structure is developed at such a junction when the outflow of majority spin electrons creates a cloud of minority spin electrons in the nonmagnetic semiconductor region near the junction. The presence of charge accumulated and depleted layers at the junction is observed to significantly modify the critical current density compared to that at charge neutral condition. The physical reason is investigated.