Understanding and optimizing spin injection in self-assembled InAs/GaAs quantum-dot molecular structures
2016 (English)In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 9, no 3, 602-611 p.Article in journal (Refereed) Published
Semiconductor quantum-dot (QD) structures are promising for spintronic applications owing to strong quenching of spin relaxation processes promoted by carrier and excitons motions. Unfortunately, spin injection efficiency in such nanostructures remains very low and the exact physical mechanism for the spin loss is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QDs and quantum-dot molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer immediately surrounding QDs and QMSs that in fact lack the commonly believed 2D and 3D character with an extended wavefunction. We identify the microscopic origin of the observed severe spin loss during spin injection as being due to a sizable anisotropic exchange interaction (AEI) of the localized excitons in the WL and GaAs barrier layer, which has so far been overlooked. We find that the AEI of the injected excitons and thus the efficiency of the spin injection processes are correlated with the overall geometric symmetry of the QMSs, as the latter largely defines the anisotropy of the confinement potential of the localized excitons in the surrounding WL and GaAs barrier. These results pave the way for a better understanding of spin injection processes and the microscopic origin of spin loss in QD structures, which in turn provides a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of the QMSs thereby overcoming a major bottleneck in spintronic device applications utilizing semiconductor QDs.
Place, publisher, year, edition, pages
Tsinghua University Press, 2016. Vol. 9, no 3, 602-611 p.
Spin injection, spin loss, quantum dot, quantum - dot molecular structure, InAs/GaAs, exciton, anisotropic exchange interaction, polarization
Condensed Matter Physics
IdentifiersURN: urn:nbn:se:liu:diva-123983DOI: 10.1007/s12274-015-0940-6ISI: 000371797000002OAI: oai:DiVA.org:liu-123983DiVA: diva2:894799