Recent advances in nanofabrication technology have made it possible to develop novel quantum opto-electronic devices at the nanometre scale. This thesis demonstrates the ability to precisely position electrostatic gates around the periphery of a deterministically positioned semiconductor quantum dot. This work also demonstrates the first published results of InAs/InP quantum dots subject to electric fields. The InAs/InP material system is particularly attractive for fiber-based quantum cryptography since the ground-state transition can be tuned to the telecommunications wavelength of 1.55 mum. Together, this approach and material system offers a fully scalable route to sources of single photon and entangled photon pairs at telecom wavelengths or arrays of initialized single spins for applications in quantum information science.
This thesis presents a detailed study of the electronic and optical properties resulting from electrostatic gating of an individual InAs quantum dot embedded in an InP nanotemplate. The unique device geometry studied here is unprecedented and allows the application of a vertical and an in-plane lateral electric field on the same quantum dot. The results show that application of a vertical electric field along the growth direction precisely controls the charge state or number of electrostatically induced electrons. Important information on the dot morphology is obtained, implying that the InAs dot composition is uniform. In contrast, application of an in-plane lateral electric field across a single quantum dot is shown to strongly modify electron-hole wavefunction overlaps and Coulomb interactions of single excitons and biexcitons while allowing a new optically forbidden transition to appear at finite field involving an s-shell electron and p-shell hole.
Of particular significance to the scientific community is the finding that application of the lateral electric field resulted in a crossing of the exciton and biexciton optical transitions, and thus removal of the biexciton binding energy. Theoretical calculations are presented demonstrating that removal of the biexciton binding energy leads to the generation of entangled photon pairs without the need to enforce degeneracy of the two intermediate, single exciton states in the biexciton-exciton radiative cascade. The nanotemplate dimensions are also shown to directly control the biexciton binding energy. A new regime of the biexciton binding energy is studied in larger dots, demonstrating the possibility of entangled photon generation through an 'unbound' biexciton state without the requirement of post-growth tuning.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29975 |
| Date | January 2009 |
| Creators | Reimer, Michael E |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 211 p. |
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