Optical spin injection in SiGe heterostructures

We present photoluminescence (PL) and spin polarized photo-emission (SPPE) measurements performed on bulk Ge, and Ge/Si(100) epilayers. A set of bi-axially strained Ge epilayers featuring different strain levels has been deposited by low energy plasma enhanced CVD (LEPECVD) and characterized by high resolution X-ray diffraction (HR-XRD). SPPE data indicate that compressive strain effectively lifts the heavy holes - light holes degeneracy raising the polarization of injected electrons above the P=50% limit of bulk material. Circularly polarized light PL measurements performed on p-type bulk crystals confirm the suitability of Ge for spintronics application showing a robust electron spin inizialization at the direct gap of Ge and giving a lower bound value for the spin relaxation time of ≈ 230 fs.

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