Magnetophotoluminescence study of excitons confined in GaAs quantum dots

Abstract

In the field of quantum information technology, single photons are a crucial resource for realizing qubits. An advantage of a photon based qubit compared to other systems is its low interaction with the environment. This allows a decoherence free distribution of quantum states over large distances at the speed of light. Therefore, a lot of effort is put in the research of single photon-sources. Among the different systems under investigation, semiconductor quantum dots are promising candidates to act as an on-demand single photon source in advanced quantum technology applications. While photons are the ideal candidates for quantum information transport, the situation is different when it comes to quantum information storage and processing. Therefore, a transfer from one physical form to another is needed to enable quantum networks and quantum entanglement over long distances. For this purpose, electron spin states confined in quantum dots of a direct bandgap semiconductor are preferred and the conversion of photon qubits into spin qubits is necessary. However, in order to perform a conversion between photonic and spin qubits, elaborate knowledge of the response of excited states in a quantum dot to an external magnetic field is required. This response is specified by the g-factor and the diamagnetic coefficient. In this thesis magnetic field dependent photoluminescence measurements are performed to study the g-factors of different complexes as well as the diamagnetic shift of optical transitions of an optically excited gallium-arsenide (GaAs) quantum dot. There have already been researches about magneto-optical properties of quantum dots, especially for indium-gallium-arsenide (InGaAs) systems. However, similar works for droplet-etched GaAs quantum dots are still missing. While for strongly confining systems, e.g. InGaAs quantum dots the single-particle Hamiltonian is used to extract the magnetic properties, the question arises if this description is also valid for weak confinement systems like our GaAs quantum dots. This work proves that an evaluation with the single-particle picture is not reasonable. Nevertheless, by investigating the magnetic properties, the various transitions in a QD are studied and assigned to certain charge complexes.submitted by Barbara Ursula Lehner, BScUniversität Linz, Masterarbeit, 2019(VLID)459085