Charge polarisation and excited state energy level structure of silicon isolated double quantum dots

This thesis presents a simulation-supported experimental investigation into the properties of highly doped (nphosphorus ~ 2.9x1019 cm-3) n-type silicon on insulator Isolated Double Quantum Dots (IDQDs) with integrated Single Electron Transistor (SET) for charge sensing. The structures are fabricated with post oxidation island diameters of between 80 and 125nm on the same chip by means of electron beam lithography and reactive ion etching to give trench isolation. Low noise electrical measurements including microwave stimulation are performed at 4.2K through immersion in liquid helium. The main results of this investigation are described below. IDQD and SET features are successfully distinguished through the gate dependence of their DC responses, revealing the first reported observations of controlled semi-periodic charge polarisation in silicon IDQDs over a large gate range. Simulation of the observed SET-IDQD electronic response is quantitatively matched to the experiment, giving insight into the device coupling. A dynamic mechanism of charge sensing in the SET is proposed, supported by simulation. The charging energy level spacing of multiple IDQDs is quantified. The dependence of the IDQD energy level separation on the device dimensions is demonstrated experimentally, in agreement with simulation, through successful fabrication of 5 devices on the same chip for direct comparison. Probable transport through single particle excitation levels in the SET is reported for the first time in a silicon based device, exhibiting an unexpected gate dependence. Excitations in the IDQD-SET device are stimulated with microwave irradiation and their origins are distinguished through the developed gate dependence method. The existence of an energy level separation between quantised states of 55.2μeV in the IDQD is demonstrated. Further well-defined splitting of the states is measured with an energy of 1.1μeV including evidence of a complex degenerate structure, possibly associated with spin states. The strong interaction of the excitation between these states and the charging of the IDQD is demonstrated.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2006

Author dc:creator

• Tanner, Michael George

Licence

• https://www.repository.cam.ac.uk/bitstreams/8887a1c3-0459-4bf7-9ea1-f280073c5ce9/download
• http://purl.org/NET/rdflicense/allrightsreserved/

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.122038

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/390489