Electrical expression of spin accumulation in ferromagnet/semiconductor structures

TL;DR

This paper develops a quantum-mechanical and semiclassical theory to explain spin injection, extraction, and accumulation in ferromagnet/semiconductor structures, enabling electrical detection and potential memory and logic applications.

Contribution

It introduces a comprehensive quantum scattering model for spin transport at ferromagnet/semiconductor interfaces, explaining experimental phenomena and enabling multi-terminal spintronic device design.

Findings

Explains counter-intuitive spin polarization in semiconductors.

Provides a basis for electrically sensing spin accumulation.

Demonstrates potential for reprogrammable spin-based logic gates.

Abstract

We treat the spin injection and extraction via a ferromagnetic metal/semiconductor Schottky barrier as a quantum scattering problem. This enables the theory to explain a number of phenomena involving spin-dependent current through the Schottky barrier, especially the counter-intuitive spin polarization direction in the semiconductor due to current extraction seen in recent experiments. A possible explanation of this phenomenon involves taking into account the spin-dependent inelastic scattering via the bound states in the interface region. The quantum-mechanical treatment of spin transport through the interface is coupled with the semiclassical description of transport in the adjoining media, in which we take into account the in-plane spin diffusion along the interface in the planar geometry used in experiments. The theory forms the basis of the calculation of spin-dependent current flow in multi-terminal systems, consisting of a semiconductor channel with many ferromagnetic contacts attached, in which the spin accumulation created by spin injection/extraction can be efficiently sensed by electrical means. A three-terminal system can be used as a magnetic memory cell with the bit of information encoded in the magnetization of one of the contacts. Using five terminals we construct a reprogrammable logic gate, in which the logic inputs and the functionality are encoded in magnetizations of the four terminals, while the current out of the fifth one gives a result of the operation.