New approaches to injecting spin polarized currents into semiconductors

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A key ingredient for the elaboration of any semiconductor spintronics based technology is the possibility of reliable injecting a spin current of tunable polarization into the semiconductor devices. Spin injection has previously been demonstrated using bulk DMS injector layers1 or resonant tunneling diodes2. The first of these methods requires thick layers and is therefore unlikely to be useful for the tuning of spin polarized currents between various elements of a circuit, whereas the second of these methods requires a complex and well optimized layer structure which presents serious integration challenges. In the present proposal we aim to study two alternative methods, which have been theoretically proposed in the literature, to produce spin polarized currents. The first is the use of a single magnetic barrier as a spin filter3 and the second is an electrically controlled spin field effect transistor4 which would allow us to tune the polarization of the current in a fixed magnetic field. As always when working on experiments with spin polarized current, one of the challenges lies in the detection of the injection efficiency. Often, the direct transport observable is a magnetoresistance, which is then back calculated into a spin polarization using a given transport model. Since these models typically make assumptions that are not easily verified on, for example, spin scattering lengths, this can often lead to ambiguity as to whether a polarized current is truly injected. In order to address this issue, we propose a complimentary use of transport and optical techniques, studying the magnetoresistance phenomena in transport and confirming the interpretation by direct optical detection of the polarization of the carrier using magnetooptical Kerr effect measurements.