A measurement system for and the measurement system of single particle energies in quantum dots
Abstract
This thesis describes the design, development, construction and performance of an instrumentation system suitable for the measurement of single electron quantum dot devices. The inaugural measurement with this new system produced fascinating experimental data from a novel magnetic spectrometer device. This data, presented in chapter 5, suggests that it is possible to measure the single particle spacing in a 500nm quantum dot device independent of the Coulomb blockade energy and within an electron mean free path. Devices were defined on a GaAs/AlGaAs heterostructure, the interface of which formed a 2 dimensional electron gas (2DEG). The surface was patterned with metallic surface gates. On the application of a potential to the gates, the electrons were depleted from beneath the gate and the pattern was transferred to the 2DEG. The devices were fabricated in a Hall bar geometry using standard nanofabrication techniques. Measurements were performed using a 3He/4He Kelvinox 25 dilution refrigerator unit at a lattice temperature of TL45mK. Prior to the work detailed in this thesis the lowest effective electron temperature available to quantum transport researchers at Glasgow had been 1.2 Kelvin. This was achieved with the use of a pumped 4He variable temperature insert (VTI), for which 1.2K represented the lowest working temperature. Although a 3He/4He dilution unit had been available for some time, the unit had exhibited an effective electron temperature of Te>7K. As a direct…
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