Contactless Monitoring of the Diameter-Dependent Conductivity of GaAs Nanowires

Contactless monitoring with photoelectron microspectroscopy of the surface potential along individual nano-structures, created by the X-ray nanoprobe, opens exciting possibilities to examine quantitatively size- and surface-chemistry-effects on the electrical transport of semiconductor nanowires (NWs). Implementing this novel approach—which combines surface chemical microanalysis with conductivity measurements—we explored the dependence of the electrical properties of undoped GaAs NWs on the NW width, temperature and surface chemistry. By following the evolution of the Ga 3d and As 3d core level spectra, we measured the position-dependent surface potential along the GaAs NWs as a function of NW diameter, decreasing from 120 to ~20 nm, and correlated the observed decrease of the conductivity with the monotonic reduction in the NW diameter from 120 to ~20 nm. Exposure of the GaAs NWs to oxygen ambient leads to a decrease in their conductivity by up to a factor of 10, attributed to the significant decrease in the carrier density associated with the formation of an oxide shell.