GaAs1-xBix is an exciting new semiconductor alloy with numerous promising applications. Incorporation of Bi into GaAs allows for a large reduction of the GaAs bandgap per percent incorporation (7x greater than In, with modest increase in lattice size) and shows strong photoluminescence (PL) and low material degradation associated with Bi. This will allow for longer wavelength devices to be grown on GaAs substrates, than is currently possible with pseudomorphic InGaAs on GaAs. Since Bi has a strong tendency for surface segregation, the molecular beam epitaxy (MBE) growth of GaAs1-xBix is challenging. To achieve Bi incorporation, this alloy requires unconventional MBE growth conditions such as a low substrate temperature and low As overpressure. The low As:Ga flux ratio also makes Ga and Bi droplet formation a problem. Therefore careful control of growth parameters, especially the As:Ga flux ratio is necessary. In this regard reflection high-energy electron diffraction (RHEED) is used in this study as a crucial tool in locating the optimum growth conditions.

Single dye molecules at cryogenic temperatures exhibit many spectroscopic phenomena known from the study of free atoms and are thus promising candidates for experiments in fundamental quantum optics. However, the past techniques for their detection have either sacrificed information on the coherence of the excited state or have been inefficient. We are able to show that these problems can be addressed by focusing the excitation light near to the extinction cross-section of a molecule. By short optical pulses we can prepare a single quantum system in a well defined state. Two methods to detect this highly non-linear feature are introduced. These rely on time correlated single photon counting and on detecting the integrated Stokes-shifted signal. On a single molecule we are able to observe up to 5 Rabi flops. A p-pulse excitation was demonstrated with merely 500 photons. Since the coherent state preparation is highly dependent on the specific excitation strength, it is possible to optimize the position of the excitation laser exactly onto the observed single emitter. This high non-linear feature can be used for high resolution microscopy. Higher spatial frequencies in the resulting images allow superior localization accuracy with less detected photons in a shorter time. By Monte Carlo simulations we gain interesting insights on the parameters influencing the localization accuracy.