Electrical spin‐injection and depolarization mechanisms in forward biased ferromagnetic Schottky diodes

Abstract

The electroluminescence of Schottky diodes with a composite ferromagnetic contact Au/Co/Au and a near‐surface InGaAs/GaAs quantum well (QW) have been studied in magnetic fields B = 0 – 10 T and low temperature T ∼ 2 K. The emission band due to recombination of the electrically injected holes with a two‐dimensional electron gas (2DEG) in the QW shows values of a circular polarization degree PC significantly higher than that in the reference nonmagnetic Au/GaAs diode, thus evidencing efficient spin injection. The nonmonotonic behavior of PC(B) at high B correlates with a filling of the Landau levels and is attributed to the nonlinear screening of a random potential by the 2DEG. The systematic decrease of PC with increasing of the QW distance dC from the contact allows to estimate the hole transport spin‐scattering length lS ∼ 90 nm at a doping level ∼1017 cm–3. Different factors of hole spin depolarization are revealed and discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)