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Title: Investigation of the electrical properties of III-V semiconductor doped with Mn
Author: Al-Ahmadi, Noorah Ahmed
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2011
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III-V semiconductors doped with Mn atoms have been studied recently for their potential applications in spintronic devices. These materials are referred to as diluted magnetic semiconductors (DMS) or ferromagnetic semiconductors. The lattice of these materials has Mn atoms (transition metal) and due to their half filled shell carries a spin and also donates carriers, "p-type" in case of Mn doping to the semiconductor lattice. Ferromagnetism is mediated by exchange interactions between localized d electrons and p-type carriers. A high transition temperature (in fact above room temperature) called Curie point, is necessary for these materials to have a practical value. The transition temperature Tc depends on the densities of both Mn impurity and the resultant hole concentration. A low density of defects, a high crystal quality and a high concentration of Mn atoms are desirable to achieve a high Tc. Additionally, cubic (zinc blende) structure offers several advantages over the hexagonal structure normally obtained for III-V semiconductors e.g. a higher crystal symmetry, smaller effective masses, higher carrier mobility, and significantly a higher doping density-which is expected to give a higher value of Tc. Both GaMnAs and GaMnN have been the materials of choice and have been studied intensely. The problems however, are related to fabricated technique, crystal quality and achieving a high doping concentration. The materials exhibit a solubility limit beyond which doping concentration are difficult to achieve. This thesis describes the investigation of the electronic properties of the zinc blend GaMnAs and GaMnN films grown at low temperature by molecular beam epitaxy (MBE) for varies concentration of Mn doping over the temperature range 15-400 K. Metal/c-GaAs: Mn/c-GaAs:Si p n junctions were studied by the I-V, C-V and C-F methods over the temperature range 15-400 K. It was found that I-V-T data could be interpreted on the basis of a back to back diode model. The c-GaAs:Mn made a Schottky contact with the metal and a p n junction with c-GaAs:Si. It was found that for the forward bias, where metal was biased negative with respect to the GaAs:Mn, the 1- v -T data could also be analysed on the basis of a Schottky behaviour. Here ideality factor n increased and the barrier height Φb decreased with temperature. This was seen to be a consequence of TFE through the metal/GaAs barrier. This was borne out by the Richardson's plots [ln (ls/T2) versus 103/nT] which exhibited straight lines. The slope indicated the barrier heights, which ranged between 1.1-1.4 eV. The backward diode on the other hand gave a barrier height of 1.4 eV, which was compatible with the proposed model. C-V-T measurements could also be accounted for, at least qualitatively, on the basis of the proposed back to back diode model. The device structure of c-GaMnN was planar. Both the Ohmic and Schottky contact were in the same plane on the top surface. I-V measurements were performed over the temperature range 100-480 K. I-V-T was explained in the terms of the Schottky model. The current was limited, however, by the Poole-Frenkel type centres in the bulk which behaved as an insulator (high resistivity semiconductor). The C-V–T was satisfactorily accounted for on the basis of MIS/MOS model. Low temperature grown films had poor material quality which made any correlation between samples difficult.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK7800 Electronics