Spin injection from a ferromagnet into a semiconductor in the case of a rough interface

TL;DR

This paper theoretically investigates how interface roughness between a ferromagnet and a semiconductor can significantly enhance spin injection efficiency, especially when irregularities are within specific size ranges, due to local electric field modifications.

Contribution

It introduces a theoretical model showing that small interface irregularities can greatly increase spin injection efficiency through geometric and electric field effects.

Findings

Small interface irregularities can enhance spin injection efficiency.

The enhancement factor is approximately the ratio of the spin-diffusion length to the irregularity size.

For curved interfaces, the enhancement depends on the local radius of curvature.

Abstract

The effect of the interface roughness on the spin injection from a ferromagnet into a semiconductor is studied theoretically. Even a small interface irregularity can lead to a significant enhancement of the injection efficiency. When a typical size of the irregularity, a, is within a domain lambda_F << a << lambda_N, where lambda_F and lambda_N are the spin-diffusion lengths in the ferromagnet and semiconductor, respectively, the geometrical enhancement factor is ~lambda_N. The origin of the enhancement is the modification of the local electric field on small scales ~a near the interface. We demonstrate the effect of enhancement by considering a number of analytically solvable examples of injection through curved ferromagnet-semiconductor interfaces. For a generic curved interface the enhancement factor is ~lambda_N / R, where R is the local radius of curvature.