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Resonant tunnelling in GaAs/AlGaAs triple barrier heterostructures

Allford, Craig ORCID: 2016. Resonant tunnelling in GaAs/AlGaAs triple barrier heterostructures. PhD Thesis, Cardiff University.
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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 effect of charge accumulation in the emitter quantum well has been investigated, and has been found to significantly 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.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: Resonant Tunnelling, Triple Barrier Heterostructures, Double Quantum Well, RTD, THz emitters
Funders: EPSRC, School of Physics and Astronomy
Date of First Compliant Deposit: 23 May 2016
Last Modified: 01 Nov 2022 10:21

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