We present a complete description of spin injection and detection in Fe/Al x Ga 1−x As/GaAs heterostructures for temperatures from 2 to 295 K. Measurements of the steady-state spin polarization in the semiconductor indicate three temperature regimes for spin transport and relaxation.At temperatures below 70 K, spin-polarized electrons injected into quantum well structures form excitons, and the spin polarization in the quantum well depends strongly on the electrical bias conditions. At intermediate temperatures, the spin polarization is determined primarily by the spin relaxation rate for free electrons in the quantum well. This process is slow relative to the excitonic spin relaxation rate at lower temperatures and is responsible for a broad maximum in the spin polarization between 100 and 200 K. The spin injection efficiency of the Fe/Al x Ga 1−x As Schottky barrier decreases at higher temperatures, although a steady-state spin polarization of at least 6% is observed at 295 K.

Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-nAl0.1Ga0.9As∕GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.

Electrical spin injection from Fe into AlxGa1−xAs quantum well heterostructures is demonstrated in small (< 500 Oe) in-plane magnetic fields. The measurement is sensitive only to the component of the spin that precesses about the internal magnetic field in the semiconductor. This field is much larger than the applied field and depends strongly on the injection current density. Details of the observed hysteresis in the spin injection signal are reproduced in a model that incorporates the magnetocrystalline anisotropy of the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamical polarization of nuclei by the injected spins.PACS numbers: 72.25. Hg, 72.25.Rb, 76.60.Jx The injection of spin from a conventional ferromagnetic metal into a semiconductor is a prerequisite for several proposed magneto-electronic devices [1]. Although spin transport across the ferromagnet-semiconductor (FM-S) interface has recently been demonstrated [2,3,4,5], most injection experiments on metallic FM-S systems have required relatively large magnetic fields, in excess of several kilogauss, to produce a spin component perpendicular to the FM-S interface. The most useful properties of typical ferromagnetic thin films, however, such as low-field switching and hysteresis, can be exploited only by coupling to the in-plane component of the magnetization [6]. In the case of metallic FM-S structures, in-plane coupling has been observed only as a small change in transport properties [2] or using optically pumped carriers [7,8].In this Letter we report a demonstration of electrical spin injection in FM-S heterostructures using small (< 500 Oe) in-plane magnetic fields. We measure only the component of the spin that precesses after injection into the semiconductor using electroluminescence polarization (ELP) as a detection technique [6,9]. The effective magnetic field inducing the precession depends strongly on the electrical bias conditions and is dramatically enhanced at the highest injection current densities. The origin of the hysteresis in the spin polarization signal is magnetization reversal in the ferromagnet, but the magnitude and shape of the observed loops depend on the effective field in the semiconductor. Modeling based on the results of optical pumping experiments demonstrates that the origin of the large effective field is dynamical nuclear polarization due to the spin-polarized current injected from the ferromagnet [10]. This approach to dynamical nuclear polarization in semiconductors is a simple alternative to the use of optical pumping or high magnetic fields as sources of spin-polarized electrons [11,12].We report results from two heterostructures with different quantum well (QW) spin detectors. The samples are grown by molecular beam epitaxy on p + GaAs (100) substrates and consist of p-Al x Ga 1−x As/QW/n-

A novel scalable and stackable nonvolatile memory technology suitable for building fast and dense memory devices is discussed. The memory cell is built by layering a storage element and a selector. The storage element is a Phase Change Memory (PCM) cell [1] and the selector is an Ovonic Threshold Switch (OTS) [2]. The vertically integrated memory cell of one PCM and one OTS (PCMS) is embedded in a true cross point array. Arrays are stacked on top of CMOS circuits for decoding, sensing and logic functions. A RESET speed of 9 nsec and endurance of 10 6 cycles are achieved.One volt of dynamic range delineating SET vs. RESET is also demonstrated.

We have studied hyperfine interactions between spin-polarized electrons and lattice nuclei in Al0.1Ga0.9As/GaAs quantum well (QW) heterostructures. The spin-polarized electrons are electrically injected into the semiconductor heterostructure from a metallic ferromagnet across a Schottky tunnel barrier. The spin-polarized electron current dynamically polarizes the nuclei in the QW, and the polarized nuclei in turn alter the electron spin dynamics. The steady-state electron spin is detected via the circular polarization of the emitted electroluminescence. The nuclear polarization and electron spin dynamics are accurately modeled using the formalism of optical orientation in GaAs. The nuclear spin polarization in the QW is found to depend strongly on the electron spin polarization in the QW, but only weakly on the electron density in the QW. We are able to observe nuclear magnetic resonance (NMR) at low applied magnetic fields on the order of a few hundred Oe by electrically modulating the spin injected into the QW. The electrically driven NMR demonstrates explicitly the existence of a Knight field felt by the nuclei due to the electron spin.