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Title: Germanium as a platform for semiconductor spintronics
Author: Foronda, Jamie
ISNI:       0000 0004 6423 7007
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2017
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The field of semiconductor spintronics is relatively underdeveloped when compared to its metallic counterpart which has found great success in the computer storage industry in hard disk drive head technology and to a lesser extent non-volatile and robust (M)RAM. The use of semiconductors in spintronics is promising with the ability to modulate spins via a gate controlled spin-orbit interaction allowing for spintronic logic and computation devices. Combining this with dilute ferromagnetic semiconductors, which have been suggested as a base for semiconductor MRAM, it may even be possible to integrate MRAM and logic into a single chip to allow for further miniaturisation of devices. In this thesis we look into the suitability of Ge as a platform for semiconductor spintronics verses other popular alternatives such as Si and GaAs. The first section of this thesis looks at evidence of a strong spin-orbit interaction in low temperature magnetoresistance curves measured in a high mobility (777,000 cm2V-1s-1) Ge 2DHG. Despite the lack of beatings in Subnikov de Haas oscillations, which often serves as an indicator of a strong spin-orbit coupling, weak antilocalisation like behaviour is seen at low fields. The spin splitting energy extracted from the weak antilocalisation and found to be 0.8meV with a Rashba parameter of 3.2x10-28 eVm3. The spin split energy is comparable to other Ge and III-V 2DHGs, however the Rashba parameter is in fact higher, which we believe is attributed to the high level of remote doping. The second section focuses on the treatment of ferromagnet/oxide spin tunnel contacts on Ge deposited by evaporation or sputtering, both of which are common in industrial scale fabrication. Annealing XPS studies are conducted on these contacts to examine the temperature limits at which annealing treatments can be done before contacts degrade. Transition line measurements are also examined to look at the electrical characteristics of the deposited contacts. The final section focuses on the fabrication and measurements of Hanle devices on n-Ge. The extracted spin lifetimes are of the same order as those measured in similarly doped Ge devices, however strong temperature dependencies of both the spin lifetime and spin accumulation signal suggest that the signal measured is strongly influenced by local states within the oxide barrier.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TK Electrical engineering. Electronics Nuclear engineering