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

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-light emitting diode consisting of a 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 similar to 0.145 at the remnant magnetization state of the Fe layer, indicating the relatively high spin injection efficiency (equivalent to 2P(EL)/P-Fe) of 0.63. (C) 2013 AIP Publishing LLC.