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Clément Porret

Effect of manganese on the growth of silicon and germanium nanowires by molecular beam epitaxy and functionalization of germanium nanowires for spintronic applications

Published on 8 September 2011

Thesis presented September 08, 2011

Abstract:
This thesis presents a study of the Vapor-Liquid-Solid (VLS) synthesis of silicon and germanium nanowires by Molecular Beam Epitaxy and the effect of the presence of manganese on the growth properties. The presence of manganese strongly modifies the growth of nanowires and observed behaviors are very different for AuSi and AuGe systems. Silicon nanowires grown in the presence of manganese exhibit very interesting morphological and structural properties. The presence of manganese modifies AuSi droplets' diameter and allows manufacturing long nanowires with relatively small diameters. Moreover, the crystalline quality is dramatically improved as compared to that of silicon nanowires grown without manganese. In this manuscript we propose some explanation for the growth phenomena. In the case of germanium nanowires, manganese incorporation could not be obtained by concomitant deposition of germanium and manganese. Consequently, (i) the doping of germanium nanowires by ion implantation as well as (ii) germanium nanowires functionalization by core/shell Ge/GeMn heterostructures formation were considered:
- magnetization measurements performed on implanted germanium nanowires demonstrate ferromagnetic properties with Curie temperatures above 400K. This result is very promising for the processing of devices using room-temperature ferromagnetic germanium nanowires;
- in order to access Ge/GeMn nanowires magnetic properties, we processed samples to probe nanowires magnetotransport properties. Electrical resistivities of devices show that transport properties are dominated by GeMn shell layer even more at low temperature. Magnetotransport measurements done at 100K indicate magnetoresistance effects linked with nanowires ferromagnetic properties.

Keywords:
Molecular beam epitaxy, Silicon and germanium nanowires, Manganese, Magnetic semiconductor, Magnetic and magnetotransport properties

On-line thesis.