Efficient spin injection through a crystalline AlOx tunnel barrier prepared by the oxidation of an ultra-thin Al epitaxial layer on GaAs

TL;DR

This paper demonstrates that a crystalline AlOx tunnel barrier, created by oxidizing an ultra-thin Al layer on GaAs, enables efficient spin injection with high polarization, without damaging the semiconductor interface.

Contribution

The study introduces a novel oxidation method to produce a crystalline AlOx tunnel barrier that enhances spin injection efficiency in spin-LED devices.

Findings

Crystalline AlOx acts as an effective tunnel barrier for spin injection.

Achieved a circular polarization of 0.145 in electroluminescence.

Spin injection efficiency of approximately 0.63 was demonstrated.

Abstract

We report that an ultra-thin, post-oxidized aluminum epilayer grown on the AlGaAs surface works as a high-quality tunnel barrier for spin injection from a ferromagnetic metal to a semiconductor. One of the key points of the present oxidation method is the formation of the crystalline AlOx template layer without oxidizing the AlGaAs region near the Al/AlGaAs interface. The oxidized Al layer is not amorphous but show well-defined single crystalline feature reminiscent of the spinel gamma-AlOx phase. A spin-LED consisting of an Fe layer, a crystalline AlOx barrier layer, and an AlGaAs-InGaAs double hetero-structure has exhibited circularly polarized electroluminescence with circular polarization of P_{EL} = 0.145 at the remnant magnetization state of the Fe layer, indicating the relatively high spin injection efficiency (epsilon = 2P_{EL} / P_{Fe}) of 0.63.