The Crystal Structure of III-V Semiconductor Nanowires: Growth and Characterization

Abstract: This thesis concerns growth and characterization of gold-particle seeded nanowires of III-V semiconductor materials (III-V NWs). The nanowires were grown using metal-organic vapour phase epitaxy (MOVPE) and characterized by various microscopy techniques. In particular cross-sectional scanning tunnelling microscopy (XSTM) and cathodoluminescence microscopy (CL) were employed to investigate heterostructured nanowires. In addition, the formation of the crystal structure within the nanowires as an effect of growth conditions was investigated by transmission electron microscopy. This thesis first presents an extensive description of the crystal structure and phases which have been observed in III-V NWs. It then gives an overview of the main characterization methods that were used in the included papers. Another part that is included concerns epitaxial growth in general and MOVPE in particular. The last part of the thesis is an outlook in which some important questions and possible future directions are presented and discussed. The basis for this thesis is 9 appended papers: Paper I-II present results from XSTM investigations; papers III-IV and VIII-IX concerns investigations of how to control the crystal phases and the density of defects within III-V NWs; paper V present a study of the effect of gold-particle fabrication method and deposition method on MOVPE growth of GaAs NWs; papers VI-VII present measurements of the ambipolar diffusion length in III-V NWs using cathodoluminescence.