Magnetic Resonances in the circular polarization of light emitted by Fe/InAs QD spin LEDs

The circular polarization $P_{circ}$ of the light emitted from InAs QD LEDs was studied as function of applied magnetic field $B$ in the 5-75 K temperature range. The quantum dots are incorporated at the center of a GaAs quantum well of width $L_{W}$ . At$ T$ = 5 K we observed two distinct resonances in the $P_{circ}$ versus $B$ plot. For $L_{W}$ = 430 {\AA} the resonances occur at $B$ = 4.6 T (strong) and $B$ = 2.3 T (weak). The strength of the resonances depends critically on bias voltage $V$ (very pronounced at low $V $values ) The resonances become weaker with increasing temperature and disappear completely by $T$ = 60 K. No resonances were observed in LEDs in which the QDs were not incorporated in a quantum well. We propose a model that takes into account the confinement conduction subbands of the GaAs quantum well and the dependence of their energies on magnetic field. Acknowledgements: This work is supported by the DARPA SpinS Project, ONR, and NSF