Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596232
Title: Spin injection into semiconductors
Author: Aziz, A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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Abstract:
This thesis describes the studies of the spin polarized current transport across Schottky barriers. Partially spin polarized electrons (~50%) are optically excited using circularly polarized light in GaAs. Under forward bias, these electrons are detected by a ferromagnetic (FM) layer at the FM/Semiconductor (Sc) interface using the spin split density of states at the Fermi-level in the FM. On average, a 3% change in the helicity dependent photo-current is observed. This confirms that about 6% of the spin polarized electrons, excited in the GaAs layer, transport into the FM across the FM/Sc interface without loosing their spin coherence. It is observed that the efficiency of the spin polarized electron transport across the Schottky barrier increases with increasing forward bias. Photo-current measurements are also performed for different excitation energies. An unusual resonant peak in the photo-current is observed at an excitation energy 20 meV below the band gap. We associate this peak with the modulation of the Schottky barrier. Barrier modulation is due to the neutralization of the ionized donor states when electrons are photo-excited to the empty donor states in the depletion region. Our results indicate that the efficiency of the spin polarized current transport increases at this resonant peak. We explain this increase by the decrease in the spin flip scattering due to ionized impurities. One of the possible routes to study room temperature spin polarized current transport across the semiconductor is by investigating the magneto-resistive properties of the devices, where a very thin semiconductor layer is sandwiched between ferromagnetic metallic layers. In this thesis two processing techniques which can be used to sandwich a thin GaAs layer between metallic electrodes are presented. Using these techniques a GaAs layer less than 100 nm thin is sandwiched between permalloy films. These techniques can potentially be used to sandwich even thinner GaAs layers between metals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.596232  DOI: Not available
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