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Title: Resonant tunnelling in GaAs/AlGaAs triple barrier heterostructures
Author: Allford, Craig
ISNI:       0000 0004 5915 3917
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2016
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This thesis describes experimental and theoretical research into triple barrier resonant tunnelling structures which are attractive as potential high frequency oscillators in the terahertz frequency range. A lack of practical and coherent radiation emitters in this frequency range has resulted in it being named the \terahertz gap". However resonant tunnelling structures are seen as potential sources for practical solid state emitters which operate in this frequency range at room temperature. A series of symmetric and asymmetric GaAs/Al0:33Ga0:67As triple barrier resonant tunnelling structures have been studied at low temperatures to investigate the tunnelling electrical behaviour and origin of the current resonances observed in the current-voltage characteristics of these structures. The e�ect of charge accumulation in the emitter quantum well has been investigated, and has been found to signi�cantly alter the behaviour of the electrical characteristics of the structures. These investigations have provided a thorough understanding of the behaviour of these structures and has allowed for optimisation of the triple barrier design with a view to being utilised as a high frequency emitter. The current-voltage characteristics have also been studied as a function of temperature and a novel temperature dependent resonant tunnelling mechanism has been observed. The magnitude of the observed current resonance, which is associated with the energetic alignment to the n = 1 quasi-bound subband states increases with increasing sample temperature which is rare behaviour in systems dominated by quantum mechanics. Finally, the maximum oscillation frequency and output power of these resonant tunnelling structures has been calculated and an optimised triple barrier structure in which charge accumulation in the emitter quantum well does not occur has been designed. Simulated current-voltage characteristics for this design shows it improves the maximum oscillation frequency and maximum output power reported in current state of the art double barrier resonant oscillator structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics