Morphology and conductivity tuning of III-V semiconductor nanowires

Semiconductor nanowires (NWs) offer a wide range of opportunities to explore the fundamentals of the crystal growth process as well as the possibility to design and fabricate novel nano-scale devices. The rational design of these devices requires the understanding of the NW growth mechanism in order to control the NW size and morphology, the NW doping, and the ability to grow coherent heterostructures. In this thesis, we grew gold-catalyzed III-V NWs via the vapour-liquid-solid (VLS) mechanism using the metalorganic vapour phase epitaxy (MOVPE) technique. We explored the details of VLS growth mechanisms by analyzing the dependence of NW growth rate on NW diameter. We presented a systematic study of the effect of precursor chemistry (i.e. group III precursor, and CBr4 dopant) on the growth of GaAs NWs. We showed that precursor chemistry can be employed as a useful mean to grow axial or radial heterostructures. A model to estimate the critical dimensions of core/shell NWs based on elasticity theory was presented. The numerical calculations were carried out for various III-V core/shell NWs and showed excellent agreement with experimental results obtained for various core/shell NWs. We demonstrated both core and shell doping of GaAs NWs using Te- (n-type) and C- (p-type) dopants. Electrical measurements were performed using a nanoprobe within a scanning electron microscope on individual NWs and doping levels and conduction mechanisms were determined. The incorporation pathways of dopants into the NWs were discussed based on the analysis of the observed dependence of measured resistivity on NW diameter.