Spin Polarization Measurements of InAs-Based LEDs

We have investigated electroluminescence (EL) characteristics of hybrid II–VI/III–V light emitting diodes (LEDs) at low temperatures and in magnetic fields up to 10 T. Spin-polarized or unpolarized electrons are injected from n-type Cd(Mn)Se layers into a wide quantum well of InAs where they undergo radiative recombination with unpolarized holes injected via p-type InAs/AlAsSb layers. Measurements of the circular polarization properties of the emitted mid-infrared EL have been made to investigate spin-injection from the Brillouin paramagnet CdMnSe into InAs; a “non-magnetic” CdSe injector is used for comparison. To infer spin polarization from the circular polarization degree, details of the InAs band structure in a magnetic field have to be taken into account due to the large electron g-factors and, more importantly, because radiative recombination and spin relaxation of injected carriers occur on similar timescales. As a result optical and spin polarization are not simply related to each other. Experimentally, the circular polarization degrees of magnetic and non-magnetic structures are observed to be very similar. In addition, broad, multi-component EL features, as well as significant carrier heating complicate the quantitative analysis.

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