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Title: Electron transport in coupled one- and two-dimensional systems
Author: Castleton, I. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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In this dissertation, transport measurements are presented on the coupling between two closely separated two-dimensional electron gases (2DEGs) formed within GaAs/AlGaAs heterostructures. The experiments fall into three main areas. Firstly, the electrical properties of a new type of switching transistor are investigated. A 2DEG is formed at the inverted and non-inverted heterojunction of a wide GaAs/AlGaAs quantum well. With the use of front and back gates, charge is moved from one 2DEG to the other in a manner similar to that proposed theoretically in the Velocity Modulated Transistor (VMT) device concept. In the VMT, switching is obtained through a mobility modulation rather than through a more conventional carrier density modulation, thereby minimising capacitive time delays. By adjusting the grown-in carrier density and mobility of each 2DEG, successful VMT operation is demonstrated, and a mobility modulation of a factor of 125 is achieved. In the second part, the resistance resonance in strongly coupled double 2DEGs is investigated. The size of the resistance resonance in three samples is measured as a function of the 2DEG mobility ratio, and the results are compared with predictions made by classical and quantum transport theories. Quenching of the resistance resonance by an in-plane magnetic field is observed, and the low- and high-field magnetoresistance are explained by considering the field-induced distortions of the Fermi surface. Finally, the transport properties of structures containing double quasi-1D wires are studied. The wires are formed by laterally confining two 2DEGs using a single Schottky split-gate. Ballistic quantisation in units of 2e2/h and 4e2/h is observed in widely spaced, non-interacting wires, while closely spaced wires are used to investigate the effects of wavefunction hybridisation in reduced dimensionality. Variations in the screening of a single quasi-1D wire are revealed by compressibility measurements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available