Spin-polarized electron transport at ferromagnet/semiconductor Schottky contacts

We theoretically investigate electron spin-injection and spin-polarization sensitive current detection at a Schottky contact between a ferromagnetic metal and an n-type or a p-type semiconductor. We use spin-dependent continuity equations and transport equations at the drift-diffusion level of approximation. Spin-polarized electron current and density in the semiconductor are described for four scenarios corresponding to the injection or the collection of spin-polarized electrons at Schottky contacts to n-type or p-type semiconductors. The transport properties of the interface are described by a spin-dependent interface resistance, resulting from an interfacial tunneling region. The spin-dependent interface resistance is crucial for achieving spin-injection or spin-polarization sensitivity in these configurations. We find that the depletion region resulting from the Schottky barrier formation at a metal/semiconductor interface is detrimental to both spin injection and spin detection. However, the depletion region can be tailored using a doping density profile to minimize these deleterious effects. For example, a heavily doped region near the interface, such as a $\delta$-doped layer, can be used to form a sharp potential profile through which electrons tunnel to reduce the effective Schottky energy barrier that determines the width of the depletion region. The model results indicate that efficient spin-injection and spin-polarization detection can be achieved in properly designed structures and can serve as a guide for the structure design.