We present a systematic study of the properties of TiN films by varying the deposition conditions in an ultra-high-vacuum reactive magnetron sputtering chamber. By increasing the deposition pressure from 2 to 9 mTorr while keeping a nearly stoichiometric composition of Ti 1−x N x (x=0.5), the film resistivity increases, the dominant crystal orientation changes from (100) to (111), grain boundaries become clearer, and the strong compressive in-plane strain changes to weak tensile in-plane strain. The TiN films absorb a high concentration of contaminants including hydrogen, carbon, and oxygen when they are exposed to air after deposition. With the target-substrate distance set to 88 mm the contaminant levels increase from ∼ 0.1% to ∼ 10% as the pressure is increased from 2 to 9 mTorr. The contaminant concentrations also correlate with in-plane distance from the center of the substrate and increase by roughly two orders of magnitude as the target-substrate distance is increased from 88 mm to 266 mm. These contaminants are found to strongly influence the properties of TiN thin films. For instance, the resistivity of stoichiometric films increases by around a factor of 5 as the oxygen content increases from 0.1% to 11%. These results strongly suggest that the energy of the sputtered TiN particles plays a crucial role in determining the TiN film properties, and that it is important to precisely control the energy of these particles to obtain high-quality TiN films. Superconducting coplanar waveguide resonators made from a series of nearly stoichiometric films grown at pressures from 2 mTorr to 7 mTorr show a substantial increase in intrinsic quality factor from ∼ 10 4 to ∼ 10 6 as the magnitude of the compressive strain decreases from nearly 3800 MPa to approximately 150 MPa and the oxygen content increases from 0.1% to 8%. The films with a higher oxygen content exhibit lower loss, but the nonuniformity of the oxygen incorporation, which presents as a radially dependent resistivity, hinders the use of reactively sputtered TiN in larger circuits.

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-

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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.

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