Alexandria Digital Research Library

Spin Engineering in Quantum Wells and Ferromagnetic Semiconductors

Mack, Shawn
Degree Grantor:
University of California, Santa Barbara. Materials
Degree Supervisor:
David D. Awschalom and Arthur C. Gossard
Place of Publication:
[Santa Barbara, Calif.]
University of California, Santa Barbara
Creation Date:
Issued Date:
Physics, Condensed Matter and Engineering, Materials Science
Molecular beam epitaxy
Dissertations, Academic and Online resources
Ph.D.--University of California, Santa Barbara, 2012

Spin engineering in semiconductors offers the potential of hybrid devices combining the useful properties of semiconductors and magnetic materials. Contemporary electronics do not utilize the spin degree of freedom in electrons, instead operating completely on the accumulation and transport of its charge by taking advantage of the wide conductivity tuning possible in semiconductors. Magnetic memory devices are not tunable, but utilize remanent magnetization to store and read information. The utilization of spins in semiconductors is a proposed route towards low-power computing and quantum computing as well as improved on-chip storage and communications schemes collectively described as "semiconductor spintronics." However, semiconductor spintronic materials are presently under development and not commercially applicable at present. Here we describe two routes of spin engineering in GaAs through the growth of heterostructures and alloys by molecular beam epitaxy.

An alloy of GaAs with manganese, Ga1-xMnxAs, displays carrier-mediated ferromagnetic behavior. Curie temperature measurements and models suggest the possibility of enhancing the Curie temperature above room temperature, but the material suffers from poor epitaxy and phase segregation at high Mn concentrations. We demonstrate improved epitaxy, almost doubling the magnetic ion incorporation limit, with a combinatorial technique utilizing the geometry of our MBE chamber, but the resulting Curie temperatures do not conform to extrapolated trends. Additionally, scanning tunneling spectroscopy shows critical behavior in our films and provides evidence that a mean-field theoretical treatment may not sufficiently describe GaMnAs. These experiments should lead to a better understanding of ferromagnetism in semiconductors.

GaAs heterostructures have intrinsic interactions between spin and orbital angular momentum caused by bulk and structural inversion asymmetry. These interactions enable electrical manipulation of spin, but they also promote decoherence. We systematically engineer balanced bulk and structural asymmetry in GaAs quantum wells to induce a special spin-orbit effective magnetic field. We demonstrate an electron spin lifetime increase of two orders of magnitude for a special pattern of spin polarization. Our results indicate further enhancement is possible and this effect may be strong enough at room temperature for spintronic devices based on electron spin.

Physical Description:
1 online resource (171 pages)
UCSB electronic theses and dissertations
Catalog System Number:
Inc.icon only.dark In Copyright
Copyright Holder:
Shawn Mack
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