Electrical conductivity of single Be-doped GaAs nanowires

In this thesis the measurement of the current-voltage characteristics of single nanowires in their as-grown geometry is presented. The studied sample is composed by Be-doped GaAs nanowires grown on Si substrate by molecular beam epitaxy. The measurements have been performed using the two terminal and the four terminal geometry, respectively in the laboratories of Universität Siegen and of Leibniz Universität Hannover. For applications of nanowires in optoelectonic applications the knowledge of electronic properties is fundamental for device optimization. The first aim of this work is the investigation of electric properties of individual nanowires onto the same substrate. The electrical characterization has been performed measuring the current-voltage characteristics of single nanowires in the 2-terminal and 4-terminal geometry. The resistance of single nanowires onto the same substrate has been calculated by fitting the obtained characteristics using thermionic emission theory. The obtained values are different from nanowire to nanowire, meaning differences in conductivity of nanowires on the same substrate. Then, the resistance profile along single nanowires has been measured in the 2-terminal geometry. This measurement shows a quasi-exponential decrease in nanowire conductivity from the bottom to the top part of individual nanowires. The experimental results are in good agreement with numerical simulations obtained using Finite Element Method calculations. The correct implantation of nanowires onto real devices also requires the knowledge of the correlation between the mechanical stress applied to single nanowires and their electric properties. The analysis of this correlation has been performed using the 2 terminal configuration, by applying different mechanical stress to the same nanowire and measuring the current-voltage characteristic at each step. The results show an increase in conductivity of the single nanowire with the increase of the applied tension