Enhancement of the Spin Accumulation at the Interface Between a Spin-Polarized Tunnel Junction and a Semiconductor

TL;DR

This paper demonstrates a significant enhancement of spin accumulation at a ferromagnet/semiconductor interface, attributed to localized states facilitating sequential tunneling, which surpasses traditional theoretical predictions.

Contribution

It introduces a model explaining the enhanced spin accumulation via localized states and sequential tunneling, providing new insights into spin injection mechanisms.

Findings

Large voltage drop indicating increased spin accumulation

Enhancement exceeds theoretical predictions for spin injection

Model accurately reproduces experimental results

Abstract

We report on spin injection experiments at a Co/Al$_2$O$_3$/GaAs interface with electrical detection. The application of a transverse magnetic field induces a large voltage drop $\Delta V$ at the interface as high as 1.2mV for a current density of 0.34 nA.$\mu m^{-2}$. This represents a dramatic increase of the spin accumulation signal, well above the theoretical predictions for spin injection through a ferromagnet/semiconductor interface. Such an enhancement is consistent with a sequential tunneling process via localized states located in the vicinity of the Al$_2$O$_3$/GaAs interface. For spin-polarized carriers these states act as an accumulation layer where the spin lifetime is large. A model taking into account the spin lifetime and the escape tunneling time for carriers travelling back into the ferromagnetic contact reproduces accurately the experimental results.