Injection of spin polarized electrons from iron and cadmium chromium selenide ferromagnetic contacts into gallium arsenide quantum well heterostructures
Mallory, Robert C
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This dissertation is composed of three projects that are all based on the injection of spin polarized electrons into a light emitting diode structure. The injecting contacts in all cases are ferromagnetic and various parameters of the devices have been studied. The distinct projects that were carried out are described separately below: (I) The electrical injection of spin polarized electrons from the ferromagnetic semiconductor CdCr 2 Se 4 into an AlGaAs/GaAs based quantum well heterostructure has been studied. The efficiency of the device's spin injecting capabilities are determined by spectroscopically analyzing the emitted light from the device. From the magnitude of the measured optical circular polarization we can determine the lower bound for the electrical injection efficiency from the ferromagnetic contact. (II) The observation of spectral features known as satellites in the Electroluminescene (EL) from Fe based spin-Light Emitting Diodes (spin-LEDs) which were based on the same AlGaAs/GaAs structure described above have been studied. The satellites are red shifted with respect to the e 1 h 1 heavy hole quantum well excitonic transition and match the energies of zone edge phonons in GaAs. A model is presented which explains the appearance of these features in the EL spectra. (III) In wide quantum well structures H-band luminescence is observed which arises from recombination between electrons and confined holes which are near the interface between GaAs and the AlGaAs(p) layers. An Oblique Hanle study has also been carried out and the spin lifetimes for various quantum well widths determined.