Quantum dots contain several isolated two-level quantum systems, an ideal starting point for the creation of a qubit. A single quantum dot embedded within a chargetunable heterostructure can be optically isolated using confocal microscopy, and electrically manipulated using an applied voltage. This thesis presents progress towards full opto-electrical control over a single dot, with a specific interest in the creation of a fully controllable electrically triggered deterministic single photon source. Polarisation control was incorporated into the confocal microscope setup, and polarisation filtering was used to enhance the signal to noise ratio in photoluminescence studies. Weierstrass solid immersion lens technology was included in the microscope design in order to improve the collection efficiency of dot photoluminescence. Static voltages were applied over single dots. Time-resolved spectroscopy allows the identification of hole tunnelling from the dot to the capping layer-superlattice interface. Suppression of hole tunnelling is achieved by altering the wafer structure. Autocorrelation measurements exhibit a finite second-order correlation at zero time delay, which is attributed to hole recapture from the wetting layer. Resonant excitation of the neutral exciton results in the creation of a negative trion in a specific voltage regime. Photolithography and electron-beam evaporation were used to manufacture several micron-scale opto-electronic devices. Several changes were made with the intention of reducing the resistance and capacitance of the device, with respect to the original macroscopic design. Photoluminescence measurements show that single dots in the new devices are capable of responding to GHz bandwidth voltage pulses. Finally, GHz bandwidth voltage pulses were applied to several single quantum dots. Single and multiple electron charging was observed on the timescale of exciton recombination. Several memory bit variations were demonstrated, each with an electrically triggered read-out mechanism. Two electrically triggered deterministic single photon sources were demonstrated, one using CW non-resonant optical excitation, the other using pulsed resonant optical excitation. Lastly, rapid adiabatic passage was attempted, with mixed results.

Semiconductor optical microcavities that combine high Q-factors with a small mode volume play a vital role in modifying the interaction between light and matter. Several interesting phenomena arise when an emitter is introduced into such a cavity. These include enhancement or suppression of the spontaneous emission rate (weak coupling) and normal mode splitting (strong coupling). In order to fully exploit the high Q and low mode volume of current microcavities, it is crucial for the emitter to be resonant with the cavity mode. Furthermore the emitter must be located at the exact antinode of the cavity electric eld. Wavelength tuning in semiconductor monolithic microcavities is challenging and is traditionally achieved by altering the temperature or using the Stark shift to alter the emitter's wavelength. Spatially matching the emitter to the electric eld antinode in monolithic cavities is even more challenging. The work in this thesis addresses these challenges. The realisation of a miniaturised, fully tunable Fabry-P erot type microcavity for semiconductor quantum dot experiments is presented. The cavity has a high Q-factor and low mode volume. The cavity wavelength is tuned by altering the air gap between the mirrors to vary the cavity length. This allows a much broader tuning range than is possible using monolithic cavities. In this work the cavity modes are characterised using a xed wavelength laser technique and varying the cavity length. A high nesse is obtained by using a miniaturised concave mirror which laterally con nes the optical mode. Unprecedented in situ control over a single InAs/GaAs quantum dot within the cavity mode is demonstrated at 4 K. The Purcell e ect is demonstrated for a single quantum dot, spatially positioned at the exact antinode of the electric eld. The cavity beam waist at the dot layer is experimentally measured and shown to be in good agreement with the theoretical value. The cavity mode volume is calculated from the measured beam waist. The e ect of weakly coupling a single dot to the cavity transverse modes is also investigated. Photoluminesence data from a high dot density sample within the cavity is presented. An anti-crossing behaviour between an ensemble of dots and the cavity mode is demonstrated. Finally, a dot dependent Fano e ect in the absorption lineshapes in a chargetunable sample is presented. A subtle interaction with an electronic continuum is revealed. The Fano e ect is shown to become more pronounced with increasing excitation power.

Using the techniques of scanning tunnelling microscopy and spectroscopy (STM/STS), the structural and electrical properties of silicon on clean cleaved GaAs(110) surfaces were investigated on a nano-meter scale. This work was focused on the effect of cleaving-induced defects on GaAs(110) surface, the resultant silicon formation and the electrical properties of the overlayer/substrate system formed at 280°C. Localised I-V measurements, performed using STS, on atomic step defects of GaAs(110) surfaces showed a Fermi-level shifted ~0.5 and 0.8 eV towards mid-gap position for both n- and p-type substrates respectively. However, measurements taken from silicon-coated atomic steps showed that the Fermi-level reverted back towards its 'ideal' flat band position by ~0.4 eV for both substrates. Similar shifts were also observed on silicon-free as well as coated defect clusters. This behaviour was distinctively different to silicon adsorbed at defect-free surfaces. Hence, these results clearly indicated passivating properties of silicon on the defective surfaces of GaAs(110) when deposited under these conditions. Such observations were also in good agreements with results obtained on macroscopic scale using x-ray photoelectron spectroscopy (XPS). STM images obtained at submonolayer silicon coverages showed preferential adsorption of silicon nanoislands at the defective sites. This suggested that the elevated temperature growth of silicon together with the excess dangling bonds associated with the defects, provided enhanced thermodynamic conditions to induce ordered silicon growth at the surface defects and effectively mopped up the dangling bonds associated with the defects, provided enhanced thermodynamic conditions to induce ordered silicon growth at the surface defects and effectively mopped up the dangling bonds. Implications of this work for use in laser facet are discussed in this thesis. Finally, this project ended with the study of 'real' laser devices using cross-sectional STM/STS techniques. The layered laser structure, which made up of different semiconducting materials, was evident from the cross-sectional STM images. Very often, atomic steps were seen at the active region of the cleaved facets which suggested the importance of facet passivation.

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