Optical Properties of Semiconductor Quantum Dots

Abstract

This thesis presents different optical experiments performed on semiconductor quantum dots. These structures allow to confine a small number of electrons and holes to a tiny region of space, some nm across. The aim of this work was to study the basic properties of different types of quantum dots made of various materials and with different techniques. First we studied InAsP quantum dots in InP nanowires and demonstrated narrow optical transitions, with linewidths below 30 micro eV. It was also possible to produce electron-hole pairs in a given spin state and to show that, in the presence of a magnetic field, this state is preserved for a time comparable to the exciton lifetime. Measurements of the electron and hole g-factors in these dots are also presented. Other types of structures dealt in this thesis are GaAs quantum dots in AlGaAs and small InAs dots in GaAs. GaAs dots can be tuned to have optical transitions at the same energy as rubidium atoms. We studied InAs quantum rings and we observed energy oscillations that are compatible with the Aharonov-Bohm effect and that can be tuned by an electric field. The last chapter of this thesis deals with two-photon interference, a useful tool for different quantum information protocols. We demonstrated that a InAs quantum dot can emit pairs of indistiguishable photons with a delay of about 5~ns between them.