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Title: Low dimensional hybrid ferromagnetic AlGaAs/GaAs semiconductor nanostructures
Author: Ahmad, S. T.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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There has been a shift in focus towards systems that integrate “nanomagnetic” components with existing device technologies, particularly for the further miniaturisation of magnetic storage devices. This thesis presents results, analysis and conclusions of studies on novel hybrid magnetic/metallic (Au/Co/Au) compositions in conjunction with low dimensional structures AlGaAs/GaAs quantum point contacts (QPC) and quantum dots (QD). The Au/Co/Au gates are used as surface confinement gates and also to apply a local inhomogeneous magnetic strayfield. Magneto-transport measurements were performed in low temperature cryostats with a minimum temperature of 350mK. It was concluded that the gating properties of these magnetic/metallic structures was significantly poor to allow for accurate characterisation of the devices. In addition, the QPC and QD themselves showed inhomogeneous effects that were dependent on the fabrication processes and material impurities. Novel broadband microwave spectroscopy measurements were used to study the transport mechanisms of a QPC. A continuous frequency range of 1-20GHz was studied where there have been no previous investigations on such devices. The experimental setup utilizes a non-invasive microwave source via a coaxial transmission line, based on the Corbino approach. The response of the device was seen to be very sensitive to these microwaves and showed ‘aperiodic’ fluctuations in the source-drain current as a function of the frequency and the onset of negative current features. These fluctuations are determined to be a result of semi-classical chaotic trapped electrons states that can be modified by the electric field of the microwave at these frequencies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available