Spin phenomena in semiconductor quantum dots

This thesis discusses development of new semiconductor quantum dot (QD) devices and materials. Optical spectroscopy of single QDs is employed in order to investigate electronic structure and magnetic properties of these materials. First we realise self-assembled InP/GaInP QDs embedded in Schottky diode structures, with the aim to realise charge control in these nanostructures, which recently provided an important test-bed for spin phenomena on the nano-scale. By varying the bias applied to the diode, we achieve accurate control of charge states in individual QDs, and also characterise the electron-hole alignment and the lateral extent of the exciton wavefunction. Second part of the thesis explores optimum regimes for optically induced dynamic nuclear polarization (DNP) in neutral InGaAs/GaAs QDs. Very efficient DNP under ultra low optical excitation is demonstrated, and its mechanism is explained as the electron-nuclear flip-flop occurring in the second order process of the dark exciton recombination. The final part of the thesis reports on magneto-optical studies of novel individual InPAs/GaInP quantum dots studied in this work for the first time. Here the long-term aim is to realise strong carrier confinement
potentially suitable for QD operation at elevated temperatures, e.g. as a single photon emitter. Here we lay foundations for future structural studies of these dots using optically detected nuclear magnetic resonance, and explore regimes for ecient DNP in InPAs dots emitting in a wide range of wavelength 690-920 nm.