Masters Defense: Giulio Ungaretti
III-V Semiconductor Nanowires growth and characterisation
Abstact: Semiconductor nanowires, tiny and marvellous materials, have been object of intense research in the past few decades for their unique properties and possible applications. Yet, a complete understanding of the growth dynamics enabling a precise control of shape, size and composition has not been reached. This thesis reports on the fabrication of substrates for nanowire growth and X-ray studies on the dynamics of nanowire growths both topics being crucial for the fundamental understating of the mechanism of the epitaxial growth of nanowires. In-situ X-ray studies are performed with a unique set-up: a molecular beam epitaxy (MBE) system mounted on a surface diffractometer at SPring8 synchrotron, Japan.
We present the fabrication process of indium arsenide substrates that allows to control the size and the position of nanowires along with the first steps to obtain nanowire networks. Moreover we show a novel family of indium arsenide substrates with a thin film of silicon dioxide. By studying the growth dynamics we find out that it is possible to create abrupt crystal phase changes by solid phase reconstruction transitions in gold assisted indium arsenide nanowires grown with MBE. We also determine the incubation time for MBE gold assisted indium arsenide nanowire growth and we show how in-situ X-ray studies can give more informations one the growth dynamics of nanowires.