In the past decades, the research on nano-scaled III-V semiconductor based technologies and devices have been rapidly expanded. As one of the most promising nanostructures, one-dimensional (1-D) III-V semiconductor nanowires have emerged as a new class of nano-scale materials exhibiting outstanding potential as building block of future electronic and optoelectronics devices and systems. In addition, in order to describe the new physics demonstrated by nanowires, much effort has been devoted to fabricating high-quality semiconductor nanowires by employing different techniques.
One of the most precise growth techniques for growing III-V epitaxial nanowires is the metal-organic chemical vapour deposition (MOCVD) technique, using Au nanoparticles (little work has been done on using non-Au catalysts) to catalyse the growth via the vapour-liquid-solid (VLS) or vapour-solid-solid (VSS) mechanism. In a MOCVD reactor, a number of key growth parameters can be precisely controlled to grow nanowires with different morphologies and crystal structures. These key parameters are the growth temperature, the absolute flow rates of group III and group V precursors, and the V/III ratio. Previous researches have been focused on the roles of the key growth parameters in III-V nanowire growth. However, little attention on the role of the catalyst has been paid sufficiently.
The objective of this thesis is to study and investigate the role of catalysts in III-V nanowire growth. By using a range of catalysts of distribution density, different morphology and chemical compositions with precisely controlled growth parameters, the correlation between the morphological, structural and chemical characteristics of the as-grown nanowires and their catalysts will be investigated by advanced electron microscopy. The results of the study will provide insights for explaining the growth mechanisms of III-V nanowires growth, which are critical for designing high-quality nanowire based devices.