A measurement system for and the measurement system of single particle energies in quantum dots

Lister, Kevin (1999) A measurement system for and the measurement system of single particle energies in quantum dots. PhD thesis, University of Glasgow.

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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 result of the work contained within this thesis (detailed in chapter 4), the lower limit of the effective electron temperature range available was extended down to 250mK. This represents an improvement of more than an order of magnitude over the lowest effective electron temperature previously available and an improvement of >20 over that previously available within the dilution limit.

In order to achieve this improvement a systems approach was adopted. The individual subsystems associated with the design of the new measurement system were designed to work in conjunction with one another. Great care was taken with respect to referencing potentials, shielding, intrinsic noise of the electronic components used and vibration isolation in order that the measurement system imposed the minimum induced electron heating on the device under test.

Measurements were performed on quantum dot devices in the Coulomb blockade regime. Periodic peaks in the conductance of a quantum dot were observed. These conductance peaks were seen in response to an applied gate voltage, and are referred to as Coulomb oscillations. Such oscillations are a result of classical charging effects due to the addition or subtraction of a single electron to, or from, the quantum dot. These effects are a direct result of the quantisation of charge. Energy quantisation due to the confinement of the electrons wave-function, also plays a role in quantum dot devices. In the devices studied the classical charging energy, that gives rise to the Coulomb oscillations is generally an order of magnitude greater than the quantum mechanical effects that give rise to the single particle spectrum.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QC Physics
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Williamson, Dr. John G.
Date of Award: 1999
Depositing User: Mr Robbie J. Ireland
Unique ID: glathesis:1999-1594
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Feb 2010
Last Modified: 10 Dec 2012 13:43
URI: https://theses.gla.ac.uk/id/eprint/1594

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