TY  - THES
AB  - For applications of nanowires in optoelectronic devices their controlled positioning onto substrates during growth is often required, as well as the control of their polytype mixture and strain state. Therefore a deep comprehension of the growth and preparation mechanisms is essential. Multiple investigation techniques at the nano-scale have been developed nowadays with the goal to correlate the structure and the physical response of nanostructures. The first aim of this work is the structural investigation of individual nanowires grown on GaAs substrates by molecular beam epitaxy. The specific positioning of the nanowires during growth has been achieved by Au-implantation into the substrate. X-ray nano-diffraction in grazing incidence diffraction geometry was used to investigate the in-plane strain at different positions, along the growth axis of individual nanowires. It was found that the nanowires are twisted about their growth axis with respect to the substrate. As expected, the crystal lattice of the nanowires is totally relaxed. Under surface diffraction conditions, the upper most layers of the growth substrate could be investigated at the same time. Here, regions at different distances from the Au-implanted area revealed the presence of a compressive strain, decreasing further away from the nanowire base. In prior studies of semiconductor nanowires it has been shown that the value of specific physical parameters strongly differ frombulk materials. For example, the high aspect ratio and the mixture of polytypes can significantly influence electrical and optical properties of GaAs nanowires. Moreover, nanowires standing in upright position onto their growth substrate revealed their importance in modern devices. The second aim of this thesis is to correlate the electrical and structural parameters of individual as-grown nanowires onto their growth substrate. This was achieved by measuring the electrical characteristics of single nanowires in a focused ion beam chamber; and by determining their polytype composition using coplanar X-ray nano-diffraction. The nanowires measured showed differing electrical characteristics. These differences have been successfully correlated with the number of zinc-blende and twinned zinc-blende units detected within single nanowires. The combination of the described techniques represents the main challenge of this work. Besides the difficulties of identifying individual nanowires in different experimental configurations; all electrical characteristics, linked to the contacting procedure of the nanowire, had to be understood and controlled. Electronic and optoelectronic applications often require specific sample preparations. Those may include the embedding of the nanostructures in a polymer matrix and the application of a top contact. As a third aim, symmetric and asymmetric X-ray diffraction revealed indirectly the presence of a preparation-induced average initial strain in the Benzocyclobutene polymer, by measuring an ensemble of embedded GaAs nanowires. This resulted in uniaxial strained embedded nanostructures, and was found to originate from the thermal processing of the polymer. The detected compression was shown to decrease under X-ray illumination and application of an external static electric field, which lead to the formation and reorientation of polar sub-molecules in the polymer.
AU  - Bussone-Grifone, Genziana
DA  - 2014
KW  - Nanodraht
KW  - Röntgennanodiffraktion
KW  - nanowire
KW  - gallium arsenide
KW  - x-ray diffraction
KW  - optoelectronics
LA  - eng
PY  - 2014
TI  - Structure and electrical response of GaAs nanowires : looking for a correlation at the nano-scale
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:467-9136
Y2  - 2024-11-22T15:22:38
ER  -