In the first stage of this project, I first grew InAs/GaAs quantum dots (QDs) and incorporated these QDs in a voltage control structure by MBE technique. The electrical or optical injection of carriers induces charged excitons including positive and negative trions. The emissions from these excitons are resolved by micro-photoluminescence spectroscopy. Due to two possible states of electron and hole spins, most excitons in QDs are doubly degenerated. We have removed this energy degeneracy using Zeeman effect by applying a magnetic field in the growth direction. The spin state of the negative trion X- consisting of two electrons and one hole is particularly interesting because of the long coherence time of hole spins. We have completely defined this spin state by measuring the polarization of the emitted photons under applied electromagnetic fields.

The goal of the second stage of this project is to increase the intensity of the exciton emissions for applications such as high rate single photon sources or quantum communication at relatively long distances. For this purpose, we have coupled the exciton emission with high quality factor micropillars. The photoluminescence emission from a single QD is thus amplified through the Purcell effect. By including the QD in a micropillar cavity and using the Quantum Confined Stark (QCS) effect, we demonstrated the tuning of the QD emission to the cavity optical modes. Q factors of 10,000 to 20,000 and an experimental Purcell factor of 3.7 were obtained. We have demonstrated a more efficient way of using the QCS effect by growing a microcavity in which two Al0.4Ga0.6As barriers are added below and above the QD layer. This allowed an increase by more than 5 times (up to 6.5meV/V) of the QCS induced energy shift of the QD emissions.

The third project deals with the growth and characterization of InGaAs Quantum Posts (QPs). The Quantum Post is a 15nm-60nm height nanowire connecting two quantum dots at its ends. I grew these QPs by MBE technique with and without Al incorporation using a self- assembled growth process. These InGaAs QPs are suitable for applications in the THz range because the transitions between the energy levels in the conduction band of QPs are tunable in the frequency range from 1THz to 10THz. In this work, I have shown experimentally the tuning of these subband energy levels by investigating QPs grown under different conditions. The InGaAs bandgap and the QP height are shown to be critical factors for this tuning. The shape, dimensions and chemical composition of QPs are obtained using electron microscopy techniques. These parameters are important inputs for the sample design and the 8-band k.p theory used to calculate the energy levels of the QPs.

Based on our Capacitance-voltage (C-V) and THz absorption experimental results, we have proposed a charging mechanism of QPs. To increase the operating temperature of the QPs, I developed a structure to increase the lateral confinement of electron inside QPs by adding aluminum to the QP growth. Due to the Ga-Al exchange reactions and the morphology of QPs, Al adatoms migrate away from QPs and accumulate around QPs. We verified this Al redistribution using Energy-dispersive X-ray spectroscopy and showed that the Al content inside QPs is 3-4 times smaller than the Al content in the matrix QW. We have demonstrated an improvement of the QPs signal and a diminishment of he signal from the matrix QW in the macro-PL, C-V and THz absorption measurements as the Al content is increased to 10%. These experiments prove that the barrier confinement for electrons in the QPs is increased for QP samples with higher Al content at temperatures below 200K. (Abstract shortened by UMI.).