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

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 AlO x 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 γ-AlO x phase. A spin-LED consisting of an Fe layer, a crystalline AlO x 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 (≡ 2P EL / P Fe ) of 0.63.

Pure circular polarization electroluminescence at room temperature with spin-polarized light-emitting diodes

“…A 1-nm-thick crystalline γ-like AlO x tunnel barrier was then grown by the authors using a molecular beam epitaxy chamber (30) The density of interface states at the AlO x / GaAs interface has been found to be D it ∼ 3 × 10 11 cm −2 ·eV −1 (38), which is far less than that at the amorphous AlO x /GaAs interface. This was followed by the fabrication of 100-nm-thick, 40-μm-wide Au (20 nm)/Ti (5 nm)/Fe(100 nm) spin-injector stripes on top of the tunnel barrier using a separate e-beam evaporator and standard photolithography.…”

“…1A is a schematic cross-section, the cleaved GaAs (110) side wall, of the tested LED chips. They consist of a polycrystalline Fe in-plane spin injector, a crystalline γ-like AlO x tunnel barrier (30), and an epitaxial AlGaAs/GaAs/AlGaAs double heterostructure (DH) (31). A magnetization vector of the spin injector is controlled either parallel or antiparallel to the GaAs [110] axis by the technical magnetization.…”

Large and robust electrical spin injection into GaAs at zero magnetic field using an ultrathin CoFeB/MgO injector

“…According to the optical selection rules 8 in quantum well (QW)-based spin LEDs, conventional spin-injector with in-plane magnetization [9][10][11][12][13][14][15][16][17][18] cannot satisfy the practical application because a strong external magnetic field in the range of up to a few Tesla is required to rotate the magnetization into a perpendicular direction. A prerequisite to obtain optimized device functionalities is to promote a robust perpendicular magnetic anisotropy (PMA) medium up to room temperature (RT) to be used as a solid-state ferromagnetic (FM) injector electrode.…”

Circularly polarized light detector based on ferromagnet/semiconductor junctions

“…110 17 cm -3 ) / 15-nm undoped Al0.1Ga0.9As / 500-nm undoped In0.03Ga0.97As / 20-nm undoped Al0.2Ga0.8As / 500-nm p-Al0.2Ga0.8As (Be  110 18 cm -3 ) / 500-nm p-GaAs (Be  110 18 cm -3 ) / p-GaAs (001), whereas the crystalline AlOx tunnel barrier (x-AlOx) was formed at RT 15) . After the formation of the crystalline AlOx layer, the AlOx /DH sample was taken out into an air atmosphere, and transferred to a separate electron beam evaporation system in which both Fe and 30-nm Au/Ti protection layers were deposited.…”

“…2(a) is a schematic diagram of a cleaved (11  0) surface which consists of three different regions: (i) a AlGaAs/InGaAs double-heterostructure (DH) for spin generation and transport, (ii) an ultra-thin, crystalline AlOx layer to circumvent the conduction mismatch 15) , and (iii) a ferromagnetic Fe layer for spin detection. The AlOx /DH in the sample was grown on a p-type GaAs (001) substrate by molecular beam epitaxy.…”