Growth optimisation of III-V semiconductors using bismuth as a surfactant and a constituent.

Dilute bismide materials have been of interest for various applications including infra-red emitters, detectors and photovoltaics for many years. Incorporating bismuth into semiconductor materials is a challenge though, which requires abnormal growth conditions within a narrow window. This often leads to poor material quality which, despite the many reports in the literature on optimising the growth of this material; it is yet to be fully understood.

A major characteristic observed in bismide materials is the formation of a localised distribution of states above the valence band of the alloys containing it. The first experimental chapter explores this state distribution via low-temperature power-dependent photo-luminescence measurements. Through the development of an existing model and applying it to a comprehensive series gallium arsenide bismide layers the effect of growth temperature and bismuth flux on this distribution of localised states is analysed. From the modelling results it is shown that this technique can be used to predict the growth regime the layer was synthesised under and inform on the requirements for further optimising the growth conditions for devices.

The second experimental chapter investigates the impacts of bismuth in a more conventional regime. Here it is used as a surfactant during the growth of indium arsenide quantum dots on gallium arsenide at two different growth temperatures. The effect of changing the magnitude of the bismuth flux is investigated to provide deeper understanding of its influence on quantum dot nucleation. Atomic force microscopy results show that increasing the magnitude of the bismuth flux consistently increases the quantum dot height. At low growth temperatures, bismuth is shown to induce the formation of quantum dots where they would not form without it. Finally, combined surface and optical studies reveal a anomalous morphology transition in the quantum dot layer grown with a low bismuth flux at high temperature. The increased quantum dot aspect ratio in this layer is believed to be the cause of its unexpected red-shift in emission wavelength, relative to the other layers in the series.

The third experimental chapter details the growth of a quaternary alloy containing bismuth, aluminium gallium arsenide bismide. The quality of this material and the way bismuth incorporates into it is compared to gallium arsenide bismide through the use of crystallographic and ion beam techniques. Results confirm that bismuth is incorporated substitutionally as in other ternary bismuth alloys. From the measurement of bismuth contents greater than achieved in gallium arsenide it is confirmed that the pathway of bismuth incorporation is not impeded by aluminium composition and it is predicted that this alloy could be grown at higher temperatures to further improve crystal quality.