Controlled in Situ n-Doping of Silicon Nanowires during VLS Growth and Their Characterization by Scanning Spreading Resistance Microscopy

Abstract

Silicon nanowires fabricated by the VLS method were n-doped with phosphine during their growth. The doping level was controlled by tuning the P/Si ratio in the CVD reactor during the synthesis. We observed that the growth rate of silicon nanowires was dopant dependent and that even the doping level of the substrate could play a poisoning role. The nanowires were characterized before and after thermal activation by scanning spreading resistance microscopy (SSRM) in a vertical structure directly on their growth substrate, showing that thermal activation led to a significant decrease of the resistance. SSRM is a simple AFM-mode-based technique that allows us to characterize in a short time a large number of individual nanowires and to correlate their dimensions to their electrical properties. Complementary techniques including scanning electron microscopy (SEM) and Raman spectroscopy were also used for the characterization of the n-doped silicon nanowires.