A new class of half-metallic ferromagnets has been found in the zinc-blende crystal structure. The previously nonexistent zinc-blende CrAs thin films have been synthesized on GaAs (001) substrates by molecular-beam epitaxy, and show a ferromagnetic behavior at room temperature. The zinc-blende CrAs has been designed by ab initio calculations based on the local spin-density approximation, and the calculation predicts the highly spin-polarized electronic band structure.
We have succeeded in growing ferromagnetic metals (Co, Fe, and NiFe)/ Al 2 O 3 / AlGaAs heterostructures with homogeneous and flat interfaces. The electro-luminescence (EL) from the light emitting diode (LED) consisting of the metal/insulator/semiconductor (MIS) structure depends on the magnetization direction of the ferromagnetic electrode at room temperature. This fact shows that a spin-injection from the ferromagnetic metal to the semiconductor is achieved. The spin-injection efficiency is estimated to be the order of 1 % at room temperature.In recent years, a new field "spintronics", that is an idea to use the spin of electrons in electronic devices, progresses remarkably. Particularly a spin-injection from a ferromagnetic material into a semiconductor is one of the hot topics in this field. It was first realized using all-semiconducting heterostructured devices. Fiederling et al. injected spin-polarized electrons into a non-magnetic semiconductor GaAs through a II-VI diluted magnetic semiconductor Be x Mn y Zn 1-x-y Se, that was used as a spin aligner. They obtained a spin-injection efficiency of 90 % at 5 K. 1 Success of the spin-injection across the II-VI/III-V interface was also reported by Jonker et al. 2 Ohno et al. used a ferromagnetic semiconductor Ga 1-x Mn x As as a spin-polarized hole source and injected the hole into GaAs with the efficiency of about 1% at 6 K. 3 Thus these experiments were succeeded at low temperature, since magnetic semiconductors does not work at room temperature. A lot of researchers make efforts to realize room-temperature operation of the spin-injection. Ferromagnetic metals (FM) are the likeliest candidates of the room-temperature spin-injecting sources. Theoretical prediction, however, showed that the limitation of the spin-injection efficiency from a metal into a semiconductor was less than 0.1 % due to a large conductance mismatch between them. 4 On the other hand, a tunneling process can inject spin-polarized electrons, since it is not affected by the conductance mismatch. 5 Zhu et al. reported the room-temperature spin injection using a Fe/GaAs Schottky barrier contact. 6 Since they used a reverse bias condition to inject electrons into GaAs, the spin-injection was done through the tunneling process across the Schottky barrier.The injection efficiency is about 2 %.Metal-insulator-semiconductor (MIS) structures using GaAs have been investigated for a long time and various preparation methods were examined in the 1970's. The MIS structure has an advantage over the Schottky barrier in the spin-injection using the tunneling process. In this letter, preparation of a homogeneous Al 2 O 3 tunnel barrier by a 2 steps deposition method on an AlGaAs/ GaAs/ AlGaAs light emitting diode (LED) is reported. We use ferromagnetic metals as a top electrode and demonstrate the spin-dependent e lectro-luminescence (EL) at room temperature.The sample growth was performed using a multi-chamber molecular-beam epitaxy (MBE) with III-V growth, metal growth and oxidation chambers. The base pres...
Zinc-blende CrAs/GaAs multilayers were grown by molecular beam epitaxy. It was certified that each CrAs layer maintains an epitaxial relationship with the zinc-blende GaAs structure judging from the reflection high-energy electron diffraction observation. The film contains thicker zinc- blende CrAs layers in total than the CrAs thin film directly grown on the GaAs substrate which has the critical thickness of 3 nm. It was clarified that the optimum thicknesses of CrAs and GaAs to keep a good epitaxial relationship are 2 ML and 2 ML, respectively. The electronic structure of the multilayer is thought to be close to that of the (Ga, Cr)As thin film which has 50% of Cr content judging from x-ray absorption spectroscopy measurements.
Gold (Au)∕semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current–voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2T, avalanche breakdown was totally quenched. When Au-SI-GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8T.
We have succeeded in demonstrating zero-magnetic-field spin injection in metal-insulator-semiconductor (MIS) structure at room temperature using FePt/MgO/GaAs-based light-emitting diode heterojunction with out-of-plane magnetization. The spin polarization was investigated by spin-polarized electroluminescence (EL). The lower estimate injected at remanence was 1.5% and that injected at 1 T was reached up to 11.5%. The spin injection efficiency was estimated at least 29%. The bias dependence of the EL circular polarization showed that it decreases with increasing bias voltage for both at 1 T and at remanence.
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