Spin Injection from Magnetic Thin Films into Ingaas Quantum Wells: the Physics of Electron Spin Polarization in Magnetic Metals and the Injection of ... in Ferromagnetic / Semiconductor Systems

The injection of spin polarised electrons into semiconductors is a fundamentalchallenge in the emergent field of spin electronics. This work isan investigation into spin injection from magnetic thin film contactsinto (100) GaAs/InGaAs quantum wells in spin light emitting diodes(spin LEDs). This structure is relevant to many quantum dot devicelayers. The spin injection characteristics are examined as a function of photon energy, magnetic field, applied bias, externaloptical efficiency and temperature. Further, the Heusler alloys Co2TiSn and Co2CrAl are investigatedthrough ab initio electronic structure calculations as potentially highlypolarised spin injectors. Pronounced minority spin band gaps were found in these alloysand while majority spins are metallic, minority spins undergo hole-likedispersion near the Fermi level. While spin injection is observed from both Heusler alloy and Fe injectors, Fe is a moreefficient spin injector and gives room temperature results. The biasdependent spin injection shows a decrease at higher voltages due tohot electron spin transport in the semiconductor and shows similartrends for both types of spin injector.