High Optical Polarization from Electrical Spin Injection into an InGaAs QW

We have fabricated spin light emitting diodes (LEDs) with Fe as the spin injector and 100{\AA} In0.1Ga0.9As/GaAs QWs as the detector. The emission efficiency from the InGaAs QW is extremely high, with a narrow linewidth of 4meV at 5K. The free exciton exhibits 25{\%} optical polarization due to the injection of spin polarized carriers from the reverse-biased Fe Schttky contact. At low biases, a feature 10meV below the free exciton appears which exhibits a much larger polarization with a peculiar magnetic field dependence. Similar to that of the free exciton, the circular polarization of this lower energy feature first increases with magnetic field, and reaches a maximum of 67{\%} at 2.5T, indicating injection from Fe. However, this behavior is superposed on a large diamagnetic background of 21{\%}/T which dominates above 2.5T. The intensity and polarization of this feature is strongly bias dependent, and the feature disappears above 15K, suggesting that it originates from a weakly bound complex. The origin of this feature and its dependence on the magnetic field will be discussed at the meeting. Supported by ONR, NRL core funds, and NSF.