ISBN 978-3-8439-2927-1

978-3-8439-2927-1, Reihe Physik

Lennart-Knud Liefeith
Spin injection through metal-semiconductor contacts

112 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5

Zusammenfassung / Abstract

In all-electric non-local spin-valves, the spin injection into bulk GaAs in the diffusive limit and into InGaAs/InAs quantum wells at the transition of the diffusive and ballistic limit is studied. Spin-polarized currents are injected into the semiconductors through epitaxial iron electrodes. The ferromagnet/semiconductor hybrid structures are grown in vacuo in a molecular-beam-epitaxy cluster that warrants crystalline quality and contamination-free interfaces. From the hybrid structures lateral spin-valve devices are fabricated under cleanroom conditions using photolithography, electron-beam lithography and wet etching techniques. The magnetic properties of the electrodes are studied by the magneto-optical Kerr effect and by magnetic force microscopy. The electrode magnetizations demonstrate that their coercivity can be controlled by the magnetic shape anisotropy.

We observe, that the spin-injection efficiency through the Fe/GaAs Schottky contacts is strongly dependent on a post-growth low-temperature annealing at 200°C. The annealing leads either to an enhancement or to a reduction of the spin-injection efficiency. Furthermore, the spin injection revealed an unexpected bias asymmetry. A spin-injection efficiency of up to 5.5% is obtained in the limit of diffusive transport. Neither the annealing dependence nor the bias asymmetry of the spin-injection efficiency is reflected in the electric properties of the Schottky contacts. A possible explanation is the formation of spin-polarized interface states that dominate the spin injection and spin detection.