Epitaxial Fe/MgO/Ge spin-photodiodes for integrated detecion of light helicity at room temperature

We report on spin-photodiodes based on fully epitaxial Fe/MgO/Ge(001) heterostructures for the room temperature integrated detection of light helicity at a wavelength of 1300 nm. The degree of circular polarization of light is related to the spin direction of photo-excited carriers in Ge that are filtered by the MgO barrier, with probabilities differing for the two spin channels. Spin-detection experiments are performed by illuminating spin-photodiodes using left or right circularly polarized light under the application of a magnetic field parallel to the light direction and measuring the current crossing the device. We found that the maximum percentage variation of the photocurrent due to full reversal of the light helicity is on the order of 5.9% at room temperature. This variation can be attributed in part to the magnetic circular dichroism of Fe (0.8%) but mainly to the spin filtering of photo-generated carriers across the MgO barrier.